This section of the Kubernetes documentation contains tutorials.
A tutorial shows how to accomplish a goal that is larger than a single
task. Typically a tutorial has several sections,
each of which has a sequence of steps.
Before walking through each tutorial, you may want to bookmark the
Standardized Glossary page for later references.
Basics
Kubernetes Basics is an in-depth interactive tutorial that helps you understand the Kubernetes system and try out some basic Kubernetes features.
If you would like to write a tutorial, see
Content Page Types
for information about the tutorial page type.
1 - Hello Minikube
This tutorial shows you how to run a sample app
on Kubernetes using minikube and Katacoda.
Katacoda provides a free, in-browser Kubernetes environment.
Note: You can also follow this tutorial if you've installed minikube locally.
See minikube start for installation instructions.
Objectives
Deploy a sample application to minikube.
Run the app.
View application logs.
Before you begin
This tutorial provides a container image that uses NGINX to echo back all the requests.
Create a minikube cluster
Click Launch Terminal
Note: If you installed minikube locally, run minikube start. Before you run minikube dashboard, you should open a new terminal, start minikube dashboard there, and then switch back to the main terminal.
Open the Kubernetes dashboard in a browser:
minikube dashboard
Katacoda environment only: At the top of the terminal pane, click the plus sign, and then click Select port to view on Host 1.
Katacoda environment only: Type 30000, and then click Display Port.
Note:
The dashboard command enables the dashboard add-on and opens the proxy in the default web browser.
You can create Kubernetes resources on the dashboard such as Deployment and Service.
By default, the dashboard is only accessible from within the internal Kubernetes virtual network.
The dashboard command creates a temporary proxy to make the dashboard accessible from outside the Kubernetes virtual network.
To stop the proxy, run Ctrl+C to exit the process.
After the command exits, the dashboard remains running in the Kubernetes cluster.
You can run the dashboard command again to create another proxy to access the dashboard.
Open Dashboard with URL
If you don't want to open a web browser, run the dashboard command with the --url flag to emit a URL:
minikube dashboard --url
Create a Deployment
A Kubernetes Pod is a group of one or more Containers,
tied together for the purposes of administration and networking. The Pod in this
tutorial has only one Container. A Kubernetes
Deployment checks on the health of your
Pod and restarts the Pod's Container if it terminates. Deployments are the
recommended way to manage the creation and scaling of Pods.
Use the kubectl create command to create a Deployment that manages a Pod. The
Pod runs a Container based on the provided Docker image.
NAME READY UP-TO-DATE AVAILABLE AGE
hello-node 1/1 1 1 1m
View the Pod:
kubectl get pods
The output is similar to:
NAME READY STATUS RESTARTS AGE
hello-node-5f76cf6ccf-br9b5 1/1 Running 0 1m
View cluster events:
kubectl get events
View the kubectl configuration:
kubectl config view
Note: For more information about kubectl commands, see the kubectl overview.
Create a Service
By default, the Pod is only accessible by its internal IP address within the
Kubernetes cluster. To make the hello-node Container accessible from outside the
Kubernetes virtual network, you have to expose the Pod as a
Kubernetes Service.
Expose the Pod to the public internet using the kubectl expose command:
The --type=LoadBalancer flag indicates that you want to expose your Service
outside of the cluster.
The application code inside the image registry.k8s.io/echoserver only listens on TCP port 8080. If you used
kubectl expose to expose a different port, clients could not connect to that other port.
View the Service you created:
kubectl get services
The output is similar to:
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
hello-node LoadBalancer 10.108.144.78 <pending> 8080:30369/TCP 21s
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 23m
On cloud providers that support load balancers,
an external IP address would be provisioned to access the Service. On minikube,
the LoadBalancer type makes the Service accessible through the minikube service
command.
Run the following command:
minikube service hello-node
Katacoda environment only: Click the plus sign, and then click Select port to view on Host 1.
Katacoda environment only: Note the 5-digit port number displayed opposite to 8080 in services output. This port number is randomly generated and it can be different for you. Type your number in the port number text box, then click Display Port. Using the example from earlier, you would type 30369.
This opens up a browser window that serves your app and shows the app's response.
Enable addons
The minikube tool includes a set of built-in addons that can be enabled, disabled and opened in the local Kubernetes environment.
This tutorial provides a walkthrough of the basics of the Kubernetes cluster orchestration system. Each module contains some background information on major Kubernetes features and concepts, and includes an interactive online tutorial. These interactive tutorials let you manage a simple cluster and its containerized applications for yourself.
Using the interactive tutorials, you can learn to:
Deploy a containerized application on a cluster.
Scale the deployment.
Update the containerized application with a new software version.
Debug the containerized application.
The tutorials use Katacoda to run a virtual terminal in your web browser that runs Minikube, a small-scale local deployment of Kubernetes that can run anywhere. There's no need to install any software or configure anything; each interactive tutorial runs directly out of your web browser itself.
What can Kubernetes do for you?
With modern web services, users expect applications to be available 24/7, and developers expect to deploy new versions of those applications several times a day. Containerization helps package software to serve these goals, enabling applications to be released and updated without downtime. Kubernetes helps you make sure those containerized applications run where and when you want, and helps them find the resources and tools they need to work. Kubernetes is a production-ready, open source platform designed with Google's accumulated experience in container orchestration, combined with best-of-breed ideas from the community.
Learn about Kubernetes cluster and create a simple cluster using Minikube.
2.1.1 - Using Minikube to Create a Cluster
Objectives
Learn what a Kubernetes cluster is.
Learn what Minikube is.
Start a Kubernetes cluster using an online terminal.
Kubernetes Clusters
Kubernetes coordinates a highly available cluster of computers that are connected to work as a single unit. The abstractions in Kubernetes allow you to deploy containerized applications to a cluster without tying them specifically to individual machines. To make use of this new model of deployment, applications need to be packaged in a way that decouples them from individual hosts: they need to be containerized. Containerized applications are more flexible and available than in past deployment models, where applications were installed directly onto specific machines as packages deeply integrated into the host. Kubernetes automates the distribution and scheduling of application containers across a cluster in a more efficient way. Kubernetes is an open-source platform and is production-ready.
A Kubernetes cluster consists of two types of resources:
The Control Plane coordinates the cluster
Nodes are the workers that run applications
Summary:
Kubernetes cluster
Minikube
Kubernetes is a production-grade, open-source platform that orchestrates the placement (scheduling) and execution of application containers within and across computer clusters.
Cluster Diagram
The Control Plane is responsible for managing the cluster. The Control Plane coordinates all activities in your cluster, such as scheduling applications, maintaining applications' desired state, scaling applications, and rolling out new updates.
A node is a VM or a physical computer that serves as a worker machine in a Kubernetes cluster. Each node has a Kubelet, which is an agent for managing the node and communicating with the Kubernetes control plane. The node should also have tools for handling container operations, such as containerd or Docker. A Kubernetes cluster that handles production traffic should have a minimum of three nodes because if one node goes down, both an etcd member and a control plane instance are lost, and redundancy is compromised. You can mitigate this risk by adding more control plane nodes.
Control Planes manage the cluster and the nodes that are used to host the running applications.
When you deploy applications on Kubernetes, you tell the control plane to start the application containers. The control plane schedules the containers to run on the cluster's nodes. The nodes communicate with the control plane using the Kubernetes API, which the control plane exposes. End users can also use the Kubernetes API directly to interact with the cluster.
A Kubernetes cluster can be deployed on either physical or virtual machines. To get started with Kubernetes development, you can use Minikube. Minikube is a lightweight Kubernetes implementation that creates a VM on your local machine and deploys a simple cluster containing only one node. Minikube is available for Linux, macOS, and Windows systems. The Minikube CLI provides basic bootstrapping operations for working with your cluster, including start, stop, status, and delete. For this tutorial, however, you'll use a provided online terminal with Minikube pre-installed.
Now that you know what Kubernetes is, let's go to the online tutorial and start our first cluster!
Once you have a running Kubernetes cluster, you can deploy your containerized applications on top of it.
To do so, you create a Kubernetes Deployment configuration. The Deployment instructs Kubernetes
how to create and update instances of your application. Once you've created a Deployment, the Kubernetes
control plane schedules the application instances included in that Deployment to run on individual Nodes in the
cluster.
Once the application instances are created, a Kubernetes Deployment Controller continuously monitors those instances. If the Node hosting an instance goes down or is deleted, the Deployment controller replaces the instance with an instance on another Node in the cluster. This provides a self-healing mechanism to address machine failure or maintenance.
In a pre-orchestration world, installation scripts would often be used to start applications, but they did not allow recovery from machine failure. By both creating your application instances and keeping them running across Nodes, Kubernetes Deployments provide a fundamentally different approach to application management.
Summary:
Deployments
Kubectl
A Deployment is responsible for creating and updating instances of your application
Deploying your first app on Kubernetes
You can create and manage a Deployment by using the Kubernetes command line interface, Kubectl. Kubectl uses the Kubernetes API to interact with the cluster. In this module, you'll learn the most common Kubectl commands needed to create Deployments that run your applications on a Kubernetes cluster.
When you create a Deployment, you'll need to specify the container image for your application and the number of replicas that you want to run. You can change that information later by updating your Deployment; Modules 5 and 6 of the bootcamp discuss how you can scale and update your Deployments.
Applications need to be packaged into one of the supported container formats in order to be deployed on Kubernetes
For your first Deployment, you'll use a hello-node application packaged in a Docker container that uses NGINX to echo back all the requests. (If you didn't already try creating a hello-node application and deploying it using a container, you can do that first by following the instructions from the Hello Minikube tutorial).
Now that you know what Deployments are, let's go to the online tutorial and deploy our first app!
A Pod is the basic execution unit of a Kubernetes application. Each Pod represents a part of a workload that is running on your cluster. Learn more about Pods.
To interact with the Terminal, please use the desktop/tablet version
When you created a Deployment in Module 2, Kubernetes created a Pod to host your application instance. A Pod is a Kubernetes abstraction that represents a group of one or more application containers (such as Docker), and some shared resources for those containers. Those resources include:
Shared storage, as Volumes
Networking, as a unique cluster IP address
Information about how to run each container, such as the container image version or specific ports to use
A Pod models an application-specific "logical host" and can contain different application containers which are relatively tightly coupled. For example, a Pod might include both the container with your Node.js app as well as a different container that feeds the data to be published by the Node.js webserver. The containers in a Pod share an IP Address and port space, are always co-located and co-scheduled, and run in a shared context on the same Node.
Pods are the atomic unit on the Kubernetes platform. When we create a Deployment on Kubernetes, that Deployment creates Pods with containers inside them (as opposed to creating containers directly). Each Pod is tied to the Node where it is scheduled, and remains there until termination (according to restart policy) or deletion. In case of a Node failure, identical Pods are scheduled on other available Nodes in the cluster.
Summary:
Pods
Nodes
Kubectl main commands
A Pod is a group of one or more application containers (such as Docker) and includes shared storage (volumes), IP address and information about how to run them.
Pods overview
Nodes
A Pod always runs on a Node. A Node is a worker machine in Kubernetes and may be either a virtual or a physical machine, depending on the cluster. Each Node is managed by the control plane. A Node can have multiple pods, and the Kubernetes control plane automatically handles scheduling the pods across the Nodes in the cluster. The control plane's automatic scheduling takes into account the available resources on each Node.
Every Kubernetes Node runs at least:
Kubelet, a process responsible for communication between the Kubernetes control plane and the Node; it manages the Pods and the containers running on a machine.
A container runtime (like Docker) responsible for pulling the container image from a registry, unpacking the container, and running the application.
Containers should only be scheduled together in a single Pod if they are tightly coupled and need to share resources such as disk.
Node overview
Troubleshooting with kubectl
In Module 2, you used Kubectl command-line interface. You'll continue to use it in Module 3 to get information about deployed applications and their environments. The most common operations can be done with the following kubectl commands:
kubectl get - list resources
kubectl describe - show detailed information about a resource
kubectl logs - print the logs from a container in a pod
kubectl exec - execute a command on a container in a pod
You can use these commands to see when applications were deployed, what their current statuses are, where they are running and what their configurations are.
Now that we know more about our cluster components and the command line, let's explore our application.
A node is a worker machine in Kubernetes and may be a VM or physical machine, depending on the cluster. Multiple Pods can run on one Node.
Understand how labels and LabelSelector objects relate to a Service
Expose an application outside a Kubernetes cluster using a Service
Overview of Kubernetes Services
Kubernetes Pods are mortal. Pods have a lifecycle. When a worker node dies, the Pods running on the Node are also lost. A ReplicaSet might then dynamically drive the cluster back to the desired state via the creation of new Pods to keep your application running. As another example, consider an image-processing backend with 3 replicas. Those replicas are exchangeable; the front-end system should not care about backend replicas or even if a Pod is lost and recreated. That said, each Pod in a Kubernetes cluster has a unique IP address, even Pods on the same Node, so there needs to be a way of automatically reconciling changes among Pods so that your applications continue to function.
A Service in Kubernetes is an abstraction which defines a logical set of Pods and a policy by which to access them. Services enable a loose coupling between dependent Pods. A Service is defined using YAML (preferred) or JSON, like all Kubernetes objects. The set of Pods targeted by a Service is usually determined by a LabelSelector (see below for why you might want a Service without including a selector in the spec).
Although each Pod has a unique IP address, those IPs are not exposed outside the cluster without a Service. Services allow your applications to receive traffic. Services can be exposed in different ways by specifying a type in the ServiceSpec:
ClusterIP (default) - Exposes the Service on an internal IP in the cluster. This type makes the Service only reachable from within the cluster.
NodePort - Exposes the Service on the same port of each selected Node in the cluster using NAT. Makes a Service accessible from outside the cluster using <NodeIP>:<NodePort>. Superset of ClusterIP.
LoadBalancer - Creates an external load balancer in the current cloud (if supported) and assigns a fixed, external IP to the Service. Superset of NodePort.
ExternalName - Maps the Service to the contents of the externalName field (e.g. foo.bar.example.com), by returning a CNAME record with its value. No proxying of any kind is set up. This type requires v1.7 or higher of kube-dns, or CoreDNS version 0.0.8 or higher.
Additionally, note that there are some use cases with Services that involve not defining a selector in the spec. A Service created without selector will also not create the corresponding Endpoints object. This allows users to manually map a Service to specific endpoints. Another possibility why there may be no selector is you are strictly using type: ExternalName.
Summary
Exposing Pods to external traffic
Load balancing traffic across multiple Pods
Using labels
A Kubernetes Service is an abstraction layer which defines a logical set of Pods and enables external traffic exposure, load balancing and service discovery for those Pods.
Services and Labels
A Service routes traffic across a set of Pods. Services are the abstraction that allows pods to die and replicate in Kubernetes without impacting your application. Discovery and routing among dependent Pods (such as the frontend and backend components in an application) are handled by Kubernetes Services.
Services match a set of Pods using labels and selectors, a grouping primitive that allows logical operation on objects in Kubernetes. Labels are key/value pairs attached to objects and can be used in any number of ways:
Designate objects for development, test, and production
Embed version tags
Classify an object using tags
Labels can be attached to objects at creation time or later on. They can be modified at any time. Let's expose our application now using a Service and apply some labels.
In the previous modules we created a Deployment, and then exposed it publicly via a Service. The Deployment created only one Pod for running our application. When traffic increases, we will need to scale the application to keep up with user demand.
Scaling is accomplished by changing the number of replicas in a Deployment
Summary:
Scaling a Deployment
You can create from the start a Deployment with multiple instances using the --replicas parameter for the kubectl create deployment command
Scaling out a Deployment will ensure new Pods are created and scheduled to Nodes with available resources. Scaling will increase the number of Pods to the new desired state. Kubernetes also supports autoscaling of Pods, but it is outside of the scope of this tutorial. Scaling to zero is also possible, and it will terminate all Pods of the specified Deployment.
Running multiple instances of an application will require a way to distribute the traffic to all of them. Services have an integrated load-balancer that will distribute network traffic to all Pods of an exposed Deployment. Services will monitor continuously the running Pods using endpoints, to ensure the traffic is sent only to available Pods.
Scaling is accomplished by changing the number of replicas in a Deployment.
Once you have multiple instances of an Application running, you would be able to do Rolling updates without downtime. We'll cover that in the next module. Now, let's go to the online terminal and scale our application.
Users expect applications to be available all the time and developers are expected to deploy new versions of them several times a day. In Kubernetes this is done with rolling updates. Rolling updates allow Deployments' update to take place with zero downtime by incrementally updating Pods instances with new ones. The new Pods will be scheduled on Nodes with available resources.
In the previous module we scaled our application to run multiple instances. This is a requirement for performing updates without affecting application availability. By default, the maximum number of Pods that can be unavailable during the update and the maximum number of new Pods that can be created, is one. Both options can be configured to either numbers or percentages (of Pods).
In Kubernetes, updates are versioned and any Deployment update can be reverted to a previous (stable) version.
Summary:
Updating an app
Rolling updates allow Deployments' update to take place with zero downtime by incrementally updating Pods instances with new ones.
Similar to application Scaling, if a Deployment is exposed publicly, the Service will load-balance the traffic only to available Pods during the update. An available Pod is an instance that is available to the users of the application.
Rolling updates allow the following actions:
Promote an application from one environment to another (via container image updates)
Rollback to previous versions
Continuous Integration and Continuous Delivery of applications with zero downtime
If a Deployment is exposed publicly, the Service will load-balance the traffic only to available Pods during the update.
In the following interactive tutorial, we'll update our application to a new version, and also perform a rollback.
3.1.1 - Externalizing config using MicroProfile, ConfigMaps and Secrets
In this tutorial you will learn how and why to externalize your microservice’s configuration.
Specifically, you will learn how to use Kubernetes ConfigMaps and Secrets to set environment
variables and then consume them using MicroProfile Config.
Before you begin
Creating Kubernetes ConfigMaps & Secrets
There are several ways to set environment variables for a Docker container in Kubernetes,
including: Dockerfile, kubernetes.yml, Kubernetes ConfigMaps, and Kubernetes Secrets. In the
tutorial, you will learn how to use the latter two for setting your environment variables whose
values will be injected into your microservices. One of the benefits for using ConfigMaps and
Secrets is that they can be re-used across multiple containers, including being assigned to
different environment variables for the different containers.
ConfigMaps are API Objects that store non-confidential key-value pairs. In the Interactive
Tutorial you will learn how to use a ConfigMap to store the application's name. For more
information regarding ConfigMaps, you can find the documentation
here.
Although Secrets are also used to store key-value pairs, they differ from ConfigMaps in that
they're intended for confidential/sensitive information and are stored using Base64 encoding.
This makes secrets the appropriate choice for storing such things as credentials, keys, and
tokens, the former of which you'll do in the Interactive Tutorial. For more information on
Secrets, you can find the documentation here.
Externalizing Config from Code
Externalized application configuration is useful because configuration usually changes depending
on your environment. In order to accomplish this, we'll use Java's Contexts and Dependency
Injection (CDI) and MicroProfile Config. MicroProfile Config is a feature of MicroProfile, a set
of open Java technologies for developing and deploying cloud-native microservices.
CDI provides a standard dependency injection capability enabling an application to be assembled
from collaborating, loosely-coupled beans. MicroProfile Config provides apps and microservices a
standard way to obtain config properties from various sources, including the application, runtime,
and environment. Based on the source's defined priority, the properties are automatically
combined into a single set of properties that the application can access via an API. Together,
CDI & MicroProfile will be used in the Interactive Tutorial to retrieve the externally provided
properties from the Kubernetes ConfigMaps and Secrets and get injected into your application code.
Many open source frameworks and runtimes implement and support MicroProfile Config. Throughout
the interactive tutorial, you'll be using Open Liberty, a flexible open-source Java runtime for
building and running cloud-native apps and microservices. However, any MicroProfile compatible
runtime could be used instead.
Objectives
Create a Kubernetes ConfigMap and Secret
Inject microservice configuration using MicroProfile Config
Example: Externalizing config using MicroProfile, ConfigMaps and Secrets
3.1.2 - Interactive Tutorial - Configuring a Java Microservice
To interact with the Terminal, please use the desktop/tablet version
3.2 - Configuring Redis using a ConfigMap
This page provides a real world example of how to configure Redis using a ConfigMap and builds upon the Configure a Pod to Use a ConfigMap task.
Objectives
Create a ConfigMap with Redis configuration values
Create a Redis Pod that mounts and uses the created ConfigMap
Verify that the configuration was correctly applied.
Before you begin
You need to have a Kubernetes cluster, and the kubectl command-line tool must
be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a
cluster, you can create one by using
minikube
or you can use one of these Kubernetes playgrounds:
Examine the contents of the Redis pod manifest and note the following:
A volume named config is created by spec.volumes[1]
The key and path under spec.volumes[1].items[0] exposes the redis-config key from the
example-redis-config ConfigMap as a file named redis.conf on the config volume.
The config volume is then mounted at /redis-master by spec.containers[0].volumeMounts[1].
This has the net effect of exposing the data in data.redis-config from the example-redis-config
ConfigMap above as /redis-master/redis.conf inside the Pod.
Check the Redis Pod again using redis-cli via kubectl exec to see if the configuration was applied:
kubectl exec -it redis -- redis-cli
Check maxmemory:
127.0.0.1:6379> CONFIG GET maxmemory
It remains at the default value of 0:
1)"maxmemory"2)"0"
Similarly, maxmemory-policy remains at the noeviction default setting:
127.0.0.1:6379> CONFIG GET maxmemory-policy
Returns:
1)"maxmemory-policy"2)"noeviction"
The configuration values have not changed because the Pod needs to be restarted to grab updated
values from associated ConfigMaps. Let's delete and recreate the Pod:
kubectl delete pod redis
kubectl apply -f https://raw.githubusercontent.com/kubernetes/website/main/content/en/examples/pods/config/redis-pod.yaml
Now re-check the configuration values one last time:
kubectl exec -it redis -- redis-cli
Check maxmemory:
127.0.0.1:6379> CONFIG GET maxmemory
It should now return the updated value of 2097152:
1)"maxmemory"2)"2097152"
Similarly, maxmemory-policy has also been updated:
127.0.0.1:6379> CONFIG GET maxmemory-policy
It now reflects the desired value of allkeys-lru:
1)"maxmemory-policy"2)"allkeys-lru"
Clean up your work by deleting the created resources:
4.1 - Apply Pod Security Standards at the Cluster Level
Note
This tutorial applies only for new clusters.
Pod Security admission (PSA) is enabled by default in v1.23 and later, as it has
graduated to beta.
Pod Security
is an admission controller that carries out checks against the Kubernetes
Pod Security Standards when new pods are
created. This tutorial shows you how to enforce the baseline Pod Security
Standard at the cluster level which applies a standard configuration
to all namespaces in a cluster.
Kubernetes control plane is running at https://127.0.0.1:61350
CoreDNS is running at https://127.0.0.1:61350/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
Get a list of namespaces in the cluster:
kubectl get ns
The output is similar to this:
NAME STATUS AGE
default Active 9m30s
kube-node-lease Active 9m32s
kube-public Active 9m32s
kube-system Active 9m32s
local-path-storage Active 9m26s
Use --dry-run=server to understand what happens when different Pod Security Standards
are applied:
From the previous output, you'll notice that applying the privileged Pod Security Standard shows no warnings
for any namespaces. However, baseline and restricted standards both have
warnings, specifically in the kube-system namespace.
Set modes, versions and standards
In this section, you apply the following Pod Security Standards to the latest version:
baseline standard in enforce mode.
restricted standard in warn and audit mode.
The baseline Pod Security Standard provides a convenient
middle ground that allows keeping the exemption list short and prevents known
privilege escalations.
Additionally, to prevent pods from failing in kube-system, you'll exempt the namespace
from having Pod Security Standards applied.
When you implement Pod Security Admission in your own environment, consider the
following:
Based on the risk posture applied to a cluster, a stricter Pod Security
Standard like restricted might be a better choice.
Exempting the kube-system namespace allows pods to run as
privileged in this namespace. For real world use, the Kubernetes project
strongly recommends that you apply strict RBAC
policies that limit access to kube-system, following the principle of least
privilege.
To implement the preceding standards, do the following:
Create a configuration file that can be consumed by the Pod Security
Admission Controller to implement these Pod Security Standards:
Creating cluster "psa-with-cluster-pss" ...
✓ Ensuring node image (kindest/node:v1.24.0) 🖼
✓ Preparing nodes 📦
✓ Writing configuration 📜
✓ Starting control-plane 🕹️
✓ Installing CNI 🔌
✓ Installing StorageClass 💾
Set kubectl context to "kind-psa-with-cluster-pss"
You can now use your cluster with:
kubectl cluster-info --context kind-psa-with-cluster-pss
Have a question, bug, or feature request? Let us know! https://kind.sigs.k8s.io/#community 🙂
Kubernetes control plane is running at https://127.0.0.1:63855
CoreDNS is running at https://127.0.0.1:63855/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
Create the following Pod specification for a minimal configuration in the default namespace:
Warning: would violate PodSecurity "restricted:latest": allowPrivilegeEscalation != false (container "nginx" must set securityContext.allowPrivilegeEscalation=false), unrestricted capabilities (container "nginx" must set securityContext.capabilities.drop=["ALL"]), runAsNonRoot != true (pod or container "nginx" must set securityContext.runAsNonRoot=true), seccompProfile (pod or container "nginx" must set securityContext.seccompProfile.type to "RuntimeDefault" or "Localhost")
pod/nginx created
Clean up
Run kind delete cluster --name psa-with-cluster-pss and
kind delete cluster --name psa-wo-cluster-pss to delete the clusters you
created.
What's next
Run a
shell script
to perform all the preceding steps at once:
Create a Pod Security Standards based cluster level Configuration
Create a file to let API server consume this configuration
Create a cluster that creates an API server with this configuration
Set kubectl context to this new cluster
Create a minimal pod yaml file
Apply this file to create a Pod in the new cluster
4.2 - Apply Pod Security Standards at the Namespace Level
Note
This tutorial applies only for new clusters.
Pod Security admission (PSA) is enabled by default in v1.23 and later, as it
graduated to beta. Pod Security Admission
is an admission controller that applies
Pod Security Standards
when pods are created. In this tutorial, you will enforce the baseline Pod Security Standard,
one namespace at a time.
Creating cluster "psa-ns-level" ...
✓ Ensuring node image (kindest/node:v1.23.0) 🖼
✓ Preparing nodes 📦
✓ Writing configuration 📜
✓ Starting control-plane 🕹️
✓ Installing CNI 🔌
✓ Installing StorageClass 💾
Set kubectl context to "kind-psa-ns-level"
You can now use your cluster with:
kubectl cluster-info --context kind-psa-ns-level
Not sure what to do next? 😅 Check out https://kind.sigs.k8s.io/docs/user/quick-start/
Set the kubectl context to the new cluster:
kubectl cluster-info --context kind-psa-ns-level
The output is similar to this:
Kubernetes control plane is running at https://127.0.0.1:50996
CoreDNS is running at https://127.0.0.1:50996/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.
Create a namespace
Create a new namespace called example:
kubectl create ns example
The output is similar to this:
namespace/example created
Apply Pod Security Standards
Enable Pod Security Standards on this namespace using labels supported by
built-in Pod Security Admission. In this step we will warn on baseline pod
security standard as per the latest version (default value)
kubectl label --overwrite ns example \
pod-security.kubernetes.io/warn=baseline \
pod-security.kubernetes.io/warn-version=latest
Multiple pod security standards can be enabled on any namespace, using labels.
Following command will enforce the baseline Pod Security Standard, but
warn and audit for restricted Pod Security Standards as per the latest
version (default value)
Apply the pod spec to the cluster in example namespace:
kubectl apply -n example -f /tmp/pss/nginx-pod.yaml
The output is similar to this:
Warning: would violate PodSecurity "restricted:latest": allowPrivilegeEscalation != false (container "nginx" must set securityContext.allowPrivilegeEscalation=false), unrestricted capabilities (container "nginx" must set securityContext.capabilities.drop=["ALL"]), runAsNonRoot != true (pod or container "nginx" must set securityContext.runAsNonRoot=true), seccompProfile (pod or container "nginx" must set securityContext.seccompProfile.type to "RuntimeDefault" or "Localhost")
pod/nginx created
Apply the pod spec to the cluster in default namespace:
4.3 - Restrict a Container's Access to Resources with AppArmor
FEATURE STATE:Kubernetes v1.4 [beta]
AppArmor is a Linux kernel security module that supplements the standard Linux user and group based
permissions to confine programs to a limited set of resources. AppArmor can be configured for any
application to reduce its potential attack surface and provide greater in-depth defense. It is
configured through profiles tuned to allow the access needed by a specific program or container,
such as Linux capabilities, network access, file permissions, etc. Each profile can be run in either
enforcing mode, which blocks access to disallowed resources, or complain mode, which only reports
violations.
AppArmor can help you to run a more secure deployment by restricting what containers are allowed to
do, and/or provide better auditing through system logs. However, it is important to keep in mind
that AppArmor is not a silver bullet and can only do so much to protect against exploits in your
application code. It is important to provide good, restrictive profiles, and harden your
applications and cluster from other angles as well.
Objectives
See an example of how to load a profile on a node
Learn how to enforce the profile on a Pod
Learn how to check that the profile is loaded
See what happens when a profile is violated
See what happens when a profile cannot be loaded
Before you begin
Make sure:
Kubernetes version is at least v1.4 -- Kubernetes support for AppArmor was added in
v1.4. Kubernetes components older than v1.4 are not aware of the new AppArmor annotations, and
will silently ignore any AppArmor settings that are provided. To ensure that your Pods are
receiving the expected protections, it is important to verify the Kubelet version of your nodes:
kubectl get nodes -o=jsonpath=$'{range .items[*]}{@.metadata.name}: {@.status.nodeInfo.kubeletVersion}\n{end}'
AppArmor kernel module is enabled -- For the Linux kernel to enforce an AppArmor profile, the
AppArmor kernel module must be installed and enabled. Several distributions enable the module by
default, such as Ubuntu and SUSE, and many others provide optional support. To check whether the
module is enabled, check the /sys/module/apparmor/parameters/enabled file:
cat /sys/module/apparmor/parameters/enabled
Y
If the Kubelet contains AppArmor support (>= v1.4), it will refuse to run a Pod with AppArmor
options if the kernel module is not enabled.
Note: Ubuntu carries many AppArmor patches that have not been merged into the upstream Linux
kernel, including patches that add additional hooks and features. Kubernetes has only been
tested with the upstream version, and does not promise support for other features.
Container runtime supports AppArmor -- Currently all common Kubernetes-supported container
runtimes should support AppArmor, like Docker,
CRI-O or containerd.
Please refer to the corresponding runtime documentation and verify that the cluster fulfills
the requirements to use AppArmor.
Profile is loaded -- AppArmor is applied to a Pod by specifying an AppArmor profile that each
container should be run with. If any of the specified profiles is not already loaded in the
kernel, the Kubelet (>= v1.4) will reject the Pod. You can view which profiles are loaded on a
node by checking the /sys/kernel/security/apparmor/profiles file. For example:
As long as the Kubelet version includes AppArmor support (>= v1.4), the Kubelet will reject a Pod
with AppArmor options if any of the prerequisites are not met. You can also verify AppArmor support
on nodes by checking the node ready condition message (though this is likely to be removed in a
later release):
kubectl get nodes -o=jsonpath='{range .items[*]}{@.metadata.name}: {.status.conditions[?(@.reason=="KubeletReady")].message}{"\n"}{end}'
gke-test-default-pool-239f5d02-gyn2: kubelet is posting ready status. AppArmor enabled
gke-test-default-pool-239f5d02-x1kf: kubelet is posting ready status. AppArmor enabled
gke-test-default-pool-239f5d02-xwux: kubelet is posting ready status. AppArmor enabled
Securing a Pod
Note: AppArmor is currently in beta, so options are specified as annotations. Once support graduates to
general availability, the annotations will be replaced with first-class fields (more details in
Upgrade path to GA).
AppArmor profiles are specified per-container. To specify the AppArmor profile to run a Pod
container with, add an annotation to the Pod's metadata:
Where <container_name> is the name of the container to apply the profile to, and <profile_ref>
specifies the profile to apply. The profile_ref can be one of:
runtime/default to apply the runtime's default profile
localhost/<profile_name> to apply the profile loaded on the host with the name <profile_name>
unconfined to indicate that no profiles will be loaded
See the API Reference for the full details on the annotation and profile name formats.
Kubernetes AppArmor enforcement works by first checking that all the prerequisites have been
met, and then forwarding the profile selection to the container runtime for enforcement. If the
prerequisites have not been met, the Pod will be rejected, and will not run.
To verify that the profile was applied, you can look for the AppArmor security option listed in the container created event:
kubectl get events | grep Created
22s 22s 1 hello-apparmor Pod spec.containers{hello} Normal Created {kubelet e2e-test-stclair-node-pool-31nt} Created container with docker id 269a53b202d3; Security:[seccomp=unconfined apparmor=k8s-apparmor-example-deny-write]
You can also verify directly that the container's root process is running with the correct profile by checking its proc attr:
Since we don't know where the Pod will be scheduled, we'll need to load the profile on all our
nodes. For this example we'll use SSH to install the profiles, but other approaches are
discussed in Setting up nodes with profiles.
NODES=(# The SSH-accessible domain names of your nodes gke-test-default-pool-239f5d02-gyn2.us-central1-a.my-k8s
gke-test-default-pool-239f5d02-x1kf.us-central1-a.my-k8s
gke-test-default-pool-239f5d02-xwux.us-central1-a.my-k8s)for NODE in ${NODES[*]}; do ssh $NODE'sudo apparmor_parser -q <<EOF
#include <tunables/global>
profile k8s-apparmor-example-deny-write flags=(attach_disconnected) {
#include <abstractions/base>
file,
# Deny all file writes.
deny /** w,
}
EOF'done
Next, we'll run a simple "Hello AppArmor" pod with the deny-write profile:
apiVersion:v1kind:Podmetadata:name:hello-apparmorannotations:# Tell Kubernetes to apply the AppArmor profile "k8s-apparmor-example-deny-write".# Note that this is ignored if the Kubernetes node is not running version 1.4 or greater.container.apparmor.security.beta.kubernetes.io/hello:localhost/k8s-apparmor-example-deny-writespec:containers:- name:helloimage:busybox:1.28command:["sh","-c","echo 'Hello AppArmor!' && sleep 1h"]
kubectl create -f ./hello-apparmor.yaml
If we look at the pod events, we can see that the Pod container was created with the AppArmor
profile "k8s-apparmor-example-deny-write":
kubectl get events | grep hello-apparmor
14s 14s 1 hello-apparmor Pod Normal Scheduled {default-scheduler } Successfully assigned hello-apparmor to gke-test-default-pool-239f5d02-gyn2
14s 14s 1 hello-apparmor Pod spec.containers{hello} Normal Pulling {kubelet gke-test-default-pool-239f5d02-gyn2} pulling image "busybox"
13s 13s 1 hello-apparmor Pod spec.containers{hello} Normal Pulled {kubelet gke-test-default-pool-239f5d02-gyn2} Successfully pulled image "busybox"
13s 13s 1 hello-apparmor Pod spec.containers{hello} Normal Created {kubelet gke-test-default-pool-239f5d02-gyn2} Created container with docker id 06b6cd1c0989; Security:[seccomp=unconfined apparmor=k8s-apparmor-example-deny-write]
13s 13s 1 hello-apparmor Pod spec.containers{hello} Normal Started {kubelet gke-test-default-pool-239f5d02-gyn2} Started container with docker id 06b6cd1c0989
We can verify that the container is actually running with that profile by checking its proc attr:
To wrap up, let's look at what happens if we try to specify a profile that hasn't been loaded:
kubectl create -f /dev/stdin <<EOF
apiVersion:v1kind:Podmetadata:name:hello-apparmor-2annotations:container.apparmor.security.beta.kubernetes.io/hello:localhost/k8s-apparmor-example-allow-writespec:containers:- name:helloimage:busybox:1.28command:["sh","-c","echo 'Hello AppArmor!' && sleep 1h"]EOFpod/hello-apparmor-2 created
kubectl describe pod hello-apparmor-2
Name: hello-apparmor-2
Namespace: default
Node: gke-test-default-pool-239f5d02-x1kf/
Start Time: Tue, 30 Aug 2016 17:58:56 -0700
Labels: <none>
Annotations: container.apparmor.security.beta.kubernetes.io/hello=localhost/k8s-apparmor-example-allow-write
Status: Pending
Reason: AppArmor
Message: Pod Cannot enforce AppArmor: profile "k8s-apparmor-example-allow-write" is not loaded
IP:
Controllers: <none>
Containers:
hello:
Container ID:
Image: busybox
Image ID:
Port:
Command:
sh
-c
echo 'Hello AppArmor!' && sleep 1h
State: Waiting
Reason: Blocked
Ready: False
Restart Count: 0
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from default-token-dnz7v (ro)
Conditions:
Type Status
Initialized True
Ready False
PodScheduled True
Volumes:
default-token-dnz7v:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-dnz7v
Optional: false
QoS Class: BestEffort
Node-Selectors: <none>
Tolerations: <none>
Events:
FirstSeen LastSeen Count From SubobjectPath Type Reason Message
--------- -------- ----- ---- ------------- -------- ------ -------
23s 23s 1 {default-scheduler } Normal Scheduled Successfully assigned hello-apparmor-2 to e2e-test-stclair-node-pool-t1f5
23s 23s 1 {kubelet e2e-test-stclair-node-pool-t1f5} Warning AppArmor Cannot enforce AppArmor: profile "k8s-apparmor-example-allow-write" is not loaded
Note the pod status is Pending, with a helpful error message: Pod Cannot enforce AppArmor: profile "k8s-apparmor-example-allow-write" is not loaded. An event was also recorded with the same message.
Administration
Setting up nodes with profiles
Kubernetes does not currently provide any native mechanisms for loading AppArmor profiles onto
nodes. There are lots of ways to set up the profiles though, such as:
Through a DaemonSet that runs a Pod on each node to
ensure the correct profiles are loaded. An example implementation can be found
here.
At node initialization time, using your node initialization scripts (e.g. Salt, Ansible, etc.) or
image.
By copying the profiles to each node and loading them through SSH, as demonstrated in the
Example.
The scheduler is not aware of which profiles are loaded onto which node, so the full set of profiles
must be loaded onto every node. An alternative approach is to add a node label for each profile (or
class of profiles) on the node, and use a
node selector to ensure the Pod is run on a
node with the required profile.
Disabling AppArmor
If you do not want AppArmor to be available on your cluster, it can be disabled by a command-line flag:
--feature-gates=AppArmor=false
When disabled, any Pod that includes an AppArmor profile will fail validation with a "Forbidden"
error.
Note: Even if the Kubernetes feature is disabled, runtimes may still enforce the default profile. The
option to disable the AppArmor feature will be removed when AppArmor graduates to general
availability (GA).
Authoring Profiles
Getting AppArmor profiles specified correctly can be a tricky business. Fortunately there are some
tools to help with that:
aa-genprof and aa-logprof generate profile rules by monitoring an application's activity and
logs, and admitting the actions it takes. Further instructions are provided by the
AppArmor documentation.
bane is an AppArmor profile generator for Docker that uses a
simplified profile language.
To debug problems with AppArmor, you can check the system logs to see what, specifically, was
denied. AppArmor logs verbose messages to dmesg, and errors can usually be found in the system
logs or through journalctl. More information is provided in
AppArmor failures.
API Reference
Pod Annotation
Specifying the profile a container will run with:
key: container.apparmor.security.beta.kubernetes.io/<container_name>
Where <container_name> matches the name of a container in the Pod.
A separate profile can be specified for each container in the Pod.
value: a profile reference, described below
Profile Reference
runtime/default: Refers to the default runtime profile.
Equivalent to not specifying a profile, except it still
requires AppArmor to be enabled.
4.4 - Restrict a Container's Syscalls with seccomp
FEATURE STATE:Kubernetes v1.19 [stable]
Seccomp stands for secure computing mode and has been a feature of the Linux
kernel since version 2.6.12. It can be used to sandbox the privileges of a
process, restricting the calls it is able to make from userspace into the
kernel. Kubernetes lets you automatically apply seccomp profiles loaded onto a
node to your Pods and containers.
Identifying the privileges required for your workloads can be difficult. In this
tutorial, you will go through how to load seccomp profiles into a local
Kubernetes cluster, how to apply them to a Pod, and how you can begin to craft
profiles that give only the necessary privileges to your container processes.
Objectives
Learn how to load seccomp profiles on a node
Learn how to apply a seccomp profile to a container
Observe auditing of syscalls made by a container process
Observe behavior when a missing profile is specified
Observe a violation of a seccomp profile
Learn how to create fine-grained seccomp profiles
Learn how to apply a container runtime default seccomp profile
Before you begin
In order to complete all steps in this tutorial, you must install
kind and kubectl.
This tutorial shows some examples that are still beta (since v1.25) and
others that use only generally available seccomp functionality. You should
make sure that your cluster is
configured correctly
for the version you are using.
The tutorial also uses the curl tool for downloading examples to your computer.
You can adapt the steps to use a different tool if you prefer.
Note: It is not possible to apply a seccomp profile to a container running with
privileged: true set in the container's securityContext. Privileged containers always
run as Unconfined.
Download example seccomp profiles
The contents of these profiles will be explored later on, but for now go ahead
and download them into a directory named profiles/ so that they can be loaded
into the cluster.
You should see three profiles listed at the end of the final step:
audit.json fine-grained.json violation.json
Create a local Kubernetes cluster with kind
For simplicity, kind can be used to create a single
node cluster with the seccomp profiles loaded. Kind runs Kubernetes in Docker,
so each node of the cluster is a container. This allows for files
to be mounted in the filesystem of each container similar to loading files
onto a node.
You can set a specific Kubernetes version by setting the node's container image.
See Nodes within the
kind documentation about configuration for more details on this.
This tutorial assumes you are using Kubernetes v1.25.
Once you have a kind configuration in place, create the kind cluster with
that configuration:
kind create cluster --config=kind.yaml
After the new Kubernetes cluster is ready, identify the Docker container running
as the single node cluster:
docker ps
You should see output indicating that a container is running with name
kind-control-plane. The output is similar to:
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
6a96207fed4b kindest/node:v1.18.2 "/usr/local/bin/entr…" 27 seconds ago Up 24 seconds 127.0.0.1:42223->6443/tcp kind-control-plane
If observing the filesystem of that container, you should see that the
profiles/ directory has been successfully loaded into the default seccomp path
of the kubelet. Use docker exec to run a command in the Pod:
# Change 6a96207fed4b to the container ID you saw from "docker ps"docker exec -it 6a96207fed4b ls /var/lib/kubelet/seccomp/profiles
audit.json fine-grained.json violation.json
You have verified that these seccomp profiles are available to the kubelet
running within kind.
Enable the use of RuntimeDefault as the default seccomp profile for all workloads
FEATURE STATE:Kubernetes v1.25 [beta]
To use seccomp profile defaulting, you must run the kubelet with the SeccompDefaultfeature gate enabled
(this is the default). You must also explicitly enable the defaulting behavior for each
node where you want to use this with the corresponding --seccomp-defaultcommand line flag.
Both have to be enabled simultaneously to use the feature.
If enabled, the kubelet will use the RuntimeDefault seccomp profile by default, which is
defined by the container runtime, instead of using the Unconfined (seccomp disabled) mode.
The default profiles aim to provide a strong set
of security defaults while preserving the functionality of the workload. It is
possible that the default profiles differ between container runtimes and their
release versions, for example when comparing those from CRI-O and containerd.
Note: Enabling the feature will neither change the Kubernetes
securityContext.seccompProfile API field nor add the deprecated annotations of
the workload. This provides users the possibility to rollback anytime without
actually changing the workload configuration. Tools like
crictl inspect can be used to
verify which seccomp profile is being used by a container.
Some workloads may require a lower amount of syscall restrictions than others.
This means that they can fail during runtime even with the RuntimeDefault
profile. To mitigate such a failure, you can:
Run the workload explicitly as Unconfined.
Disable the SeccompDefault feature for the nodes. Also making sure that
workloads get scheduled on nodes where the feature is disabled.
Create a custom seccomp profile for the workload.
If you were introducing this feature into production-like cluster, the Kubernetes project
recommends that you enable this feature gate on a subset of your nodes and then
test workload execution before rolling the change out cluster-wide.
You can find more detailed information about a possible upgrade and downgrade strategy
in the related Kubernetes Enhancement Proposal (KEP):
Enable seccomp by default.
Kubernetes 1.25 lets you configure the seccomp profile
that applies when the spec for a Pod doesn't define a specific seccomp profile.
This is a beta feature and the corresponding SeccompDefaultfeature
gate is enabled by
default. However, you still need to enable this defaulting for each node where
you would like to use it.
If you are running a Kubernetes 1.25 cluster and want to
enable the feature, either run the kubelet with the --seccomp-default command
line flag, or enable it through the kubelet configuration
file. To enable the
feature gate in kind, ensure that kind provides
the minimum required Kubernetes version and enables the SeccompDefault feature
in the kind configuration:
kubectl run --rm -it --restart=Never --image=alpine alpine -- sh
Should now have the default seccomp profile attached. This can be verified by
using docker exec to run crictl inspect for the container on the kind
worker:
apiVersion:v1kind:Podmetadata:name:audit-podlabels:app:audit-podspec:securityContext:seccompProfile:type:LocalhostlocalhostProfile:profiles/audit.jsoncontainers:- name:test-containerimage:hashicorp/http-echo:0.2.3args:- "-text=just made some syscalls!"securityContext:allowPrivilegeEscalation:false
Note:
The functional support for the already deprecated seccomp annotations
seccomp.security.alpha.kubernetes.io/pod (for the whole pod) and
container.seccomp.security.alpha.kubernetes.io/[name] (for a single container)
is going to be removed with a future release of Kubernetes. Please always use
the native API fields in favor of the annotations.
Since Kubernetes v1.25, kubelets no longer support the annotations, use of the
annotations in static pods is no longer supported, and the seccomp annotations
are no longer auto-populated when pods with seccomp fields are created.
Auto-population of the seccomp fields from the annotations is planned to be
removed in a future release.
This profile does not restrict any syscalls, so the Pod should start
successfully.
kubectl get pod/audit-pod
NAME READY STATUS RESTARTS AGE
audit-pod 1/1 Running 0 30s
In order to be able to interact with this endpoint exposed by this
container, create a NodePort Services
that allows access to the endpoint from inside the kind control plane container.
kubectl expose pod audit-pod --type NodePort --port 5678
Check what port the Service has been assigned on the node.
kubectl get service audit-pod
The output is similar to:
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
audit-pod NodePort 10.111.36.142 <none> 5678:32373/TCP 72s
Now you can use curl to access that endpoint from inside the kind control plane container,
at the port exposed by this Service. Use docker exec to run the curl command within the
container belonging to that control plane container:
# Change 6a96207fed4b to the control plane container ID you saw from "docker ps"docker exec -it 6a96207fed4b curl localhost:32373
just made some syscalls!
You can see that the process is running, but what syscalls did it actually make?
Because this Pod is running in a local cluster, you should be able to see those
in /var/log/syslog. Open up a new terminal window and tail the output for
calls from http-echo:
tail -f /var/log/syslog | grep 'http-echo'
You should already see some logs of syscalls made by http-echo, and if you
curl the endpoint in the control plane container you will see more written.
You can begin to understand the syscalls required by the http-echo process by
looking at the syscall= entry on each line. While these are unlikely to
encompass all syscalls it uses, it can serve as a basis for a seccomp profile
for this container.
Clean up that Pod and Service before moving to the next section:
kubectl delete service audit-pod --wait
kubectl delete pod audit-pod --wait --now
Create Pod with a seccomp profile that causes violation
For demonstration, apply a profile to the Pod that does not allow for any
syscalls.
apiVersion:v1kind:Podmetadata:name:violation-podlabels:app:violation-podspec:securityContext:seccompProfile:type:LocalhostlocalhostProfile:profiles/violation.jsoncontainers:- name:test-containerimage:hashicorp/http-echo:0.2.3args:- "-text=just made some syscalls!"securityContext:allowPrivilegeEscalation:false
The Pod creates, but there is an issue.
If you check the status of the Pod, you should see that it failed to start.
kubectl get pod/violation-pod
NAME READY STATUS RESTARTS AGE
violation-pod 0/1 CrashLoopBackOff 1 6s
As seen in the previous example, the http-echo process requires quite a few
syscalls. Here seccomp has been instructed to error on any syscall by setting
"defaultAction": "SCMP_ACT_ERRNO". This is extremely secure, but removes the
ability to do anything meaningful. What you really want is to give workloads
only the privileges they need.
Clean up that Pod before moving to the next section:
kubectl delete pod violation-pod --wait --now
Create Pod with a seccomp profile that only allows necessary syscalls
If you take a look at the fine-grained.json profile, you will notice some of the syscalls
seen in syslog of the first example where the profile set "defaultAction": "SCMP_ACT_LOG". Now the profile is setting "defaultAction": "SCMP_ACT_ERRNO",
but explicitly allowing a set of syscalls in the "action": "SCMP_ACT_ALLOW"
block. Ideally, the container will run successfully and you will see no messages
sent to syslog.
apiVersion:v1kind:Podmetadata:name:fine-podlabels:app:fine-podspec:securityContext:seccompProfile:type:LocalhostlocalhostProfile:profiles/fine-grained.jsoncontainers:- name:test-containerimage:hashicorp/http-echo:0.2.3args:- "-text=just made some syscalls!"securityContext:allowPrivilegeEscalation:false
The Pod should be showing as having started successfully:
NAME READY STATUS RESTARTS AGE
fine-pod 1/1 Running 0 30s
Open up a new terminal window and use tail to monitor for log entries that
mention calls from http-echo:
# The log path on your computer might be different from "/var/log/syslog"tail -f /var/log/syslog | grep 'http-echo'
Next, expose the Pod with a NodePort Service:
kubectl expose pod fine-pod --type NodePort --port 5678
Check what port the Service has been assigned on the node:
kubectl get service fine-pod
The output is similar to:
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
fine-pod NodePort 10.111.36.142 <none> 5678:32373/TCP 72s
Use curl to access that endpoint from inside the kind control plane container:
# Change 6a96207fed4b to the control plane container ID you saw from "docker ps"docker exec -it 6a96207fed4b curl localhost:32373
just made some syscalls!
You should see no output in the syslog. This is because the profile allowed all
necessary syscalls and specified that an error should occur if one outside of
the list is invoked. This is an ideal situation from a security perspective, but
required some effort in analyzing the program. It would be nice if there was a
simple way to get closer to this security without requiring as much effort.
Clean up that Pod and Service before moving to the next section:
kubectl delete service fine-pod --wait
kubectl delete pod fine-pod --wait --now
Create Pod that uses the container runtime default seccomp profile
Most container runtimes provide a sane set of default syscalls that are allowed
or not. You can adopt these defaults for your workload by setting the seccomp
type in the security context of a pod or container to RuntimeDefault.
Note: If you have the SeccompDefaultfeature gate enabled, then Pods use the RuntimeDefault seccomp profile whenever
no other seccomp profile is specified. Otherwise, the default is Unconfined.
Here's a manifest for a Pod that requests the RuntimeDefault seccomp profile
for all its containers:
apiVersion:v1kind:Podmetadata:name:default-podlabels:app:default-podspec:securityContext:seccompProfile:type:RuntimeDefaultcontainers:- name:test-containerimage:hashicorp/http-echo:0.2.3args:- "-text=just made some more syscalls!"securityContext:allowPrivilegeEscalation:false
Use a cloud provider like Google Kubernetes Engine or Amazon Web Services to
create a Kubernetes cluster. This tutorial creates an
external load balancer,
which requires a cloud provider.
Configure kubectl to communicate with your Kubernetes API server. For instructions, see the
documentation for your cloud provider.
Objectives
Run five instances of a Hello World application.
Create a Service object that exposes an external IP address.
Use the Service object to access the running application.
Creating a service for an application running in five pods
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
my-service LoadBalancer 10.3.245.137 104.198.205.71 8080/TCP 54s
Note: The type=LoadBalancer service is backed by external cloud providers, which is not covered in this example, please refer to this page for the details.
Note: If the external IP address is shown as <pending>, wait for a minute and enter the same command again.
Make a note of the external IP address (LoadBalancer Ingress) exposed by
your service. In this example, the external IP address is 104.198.205.71.
Also note the value of Port and NodePort. In this example, the Port
is 8080 and the NodePort is 32377.
In the preceding output, you can see that the service has several endpoints:
10.0.0.6:8080,10.0.1.6:8080,10.0.1.7:8080 + 2 more. These are internal
addresses of the pods that are running the Hello World application. To
verify these are pod addresses, enter this command:
Use the external IP address (LoadBalancer Ingress) to access the Hello
World application:
curl http://<external-ip>:<port>
where <external-ip> is the external IP address (LoadBalancer Ingress)
of your Service, and <port> is the value of Port in your Service
description.
If you are using minikube, typing minikube service my-service will
automatically open the Hello World application in a browser.
The response to a successful request is a hello message:
Hello Kubernetes!
Cleaning up
To delete the Service, enter this command:
kubectl delete services my-service
To delete the Deployment, the ReplicaSet, and the Pods that are running
the Hello World application, enter this command:
5.2 - Example: Deploying PHP Guestbook application with Redis
This tutorial shows you how to build and deploy a simple (not production
ready), multi-tier web application using Kubernetes and
Docker. This example consists of the following
components:
A single-instance Redis to store guestbook entries
Multiple web frontend instances
Objectives
Start up a Redis leader.
Start up two Redis followers.
Start up the guestbook frontend.
Expose and view the Frontend Service.
Clean up.
Before you begin
You need to have a Kubernetes cluster, and the kubectl command-line tool must
be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a
cluster, you can create one by using
minikube
or you can use one of these Kubernetes playgrounds:
Query the list of Pods to verify that the Redis Pod is running:
kubectl get pods
The response should be similar to this:
NAME READY STATUS RESTARTS AGE
redis-leader-fb76b4755-xjr2n 1/1 Running 0 13s
Run the following command to view the logs from the Redis leader Pod:
kubectl logs -f deployment/redis-leader
Creating the Redis leader Service
The guestbook application needs to communicate to the Redis to write its data.
You need to apply a Service to
proxy the traffic to the Redis Pod. A Service defines a policy to access the
Pods.
Query the list of Services to verify that the Redis Service is running:
kubectl get service
The response should be similar to this:
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.0.0.1 <none> 443/TCP 1m
redis-leader ClusterIP 10.103.78.24 <none> 6379/TCP 16s
Note: This manifest file creates a Service named redis-leader with a set of labels
that match the labels previously defined, so the Service routes network
traffic to the Redis Pod.
Set up Redis followers
Although the Redis leader is a single Pod, you can make it highly available
and meet traffic demands by adding a few Redis followers, or replicas.
Verify that the two Redis follower replicas are running by querying the list of Pods:
kubectl get pods
The response should be similar to this:
NAME READY STATUS RESTARTS AGE
redis-follower-dddfbdcc9-82sfr 1/1 Running 0 37s
redis-follower-dddfbdcc9-qrt5k 1/1 Running 0 38s
redis-leader-fb76b4755-xjr2n 1/1 Running 0 11m
Creating the Redis follower service
The guestbook application needs to communicate with the Redis followers to
read data. To make the Redis followers discoverable, you must set up another
Service.
# SOURCE: https://cloud.google.com/kubernetes-engine/docs/tutorials/guestbookapiVersion:v1kind:Servicemetadata:name:redis-followerlabels:app:redisrole:followertier:backendspec:ports:# the port that this service should serve on- port:6379selector:app:redisrole:followertier:backend
Apply the Redis Service from the following redis-follower-service.yaml file:
Query the list of Services to verify that the Redis Service is running:
kubectl get service
The response should be similar to this:
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 3d19h
redis-follower ClusterIP 10.110.162.42 <none> 6379/TCP 9s
redis-leader ClusterIP 10.103.78.24 <none> 6379/TCP 6m10s
Note: This manifest file creates a Service named redis-follower with a set of
labels that match the labels previously defined, so the Service routes network
traffic to the Redis Pod.
Set up and Expose the Guestbook Frontend
Now that you have the Redis storage of your guestbook up and running, start
the guestbook web servers. Like the Redis followers, the frontend is deployed
using a Kubernetes Deployment.
The guestbook app uses a PHP frontend. It is configured to communicate with
either the Redis follower or leader Services, depending on whether the request
is a read or a write. The frontend exposes a JSON interface, and serves a
jQuery-Ajax-based UX.
Query the list of Pods to verify that the three frontend replicas are running:
kubectl get pods -l app=guestbook -l tier=frontend
The response should be similar to this:
NAME READY STATUS RESTARTS AGE
frontend-85595f5bf9-5tqhb 1/1 Running 0 47s
frontend-85595f5bf9-qbzwm 1/1 Running 0 47s
frontend-85595f5bf9-zchwc 1/1 Running 0 47s
Creating the Frontend Service
The Redis Services you applied is only accessible within the Kubernetes
cluster because the default type for a Service is
ClusterIP.
ClusterIP provides a single IP address for the set of Pods the Service is
pointing to. This IP address is accessible only within the cluster.
If you want guests to be able to access your guestbook, you must configure the
frontend Service to be externally visible, so a client can request the Service
from outside the Kubernetes cluster. However a Kubernetes user can use
kubectl port-forward to access the service even though it uses a
ClusterIP.
Note: Some cloud providers, like Google Compute Engine or Google Kubernetes Engine,
support external load balancers. If your cloud provider supports load
balancers and you want to use it, uncomment type: LoadBalancer.
# SOURCE: https://cloud.google.com/kubernetes-engine/docs/tutorials/guestbookapiVersion:v1kind:Servicemetadata:name:frontendlabels:app:guestbooktier:frontendspec:# if your cluster supports it, uncomment the following to automatically create# an external load-balanced IP for the frontend service.# type: LoadBalancer#type: LoadBalancerports:# the port that this service should serve on- port:80selector:app:guestbooktier:frontend
Apply the frontend Service from the frontend-service.yaml file:
If you deployed the frontend-service.yaml manifest with type: LoadBalancer
you need to find the IP address to view your Guestbook.
Run the following command to get the IP address for the frontend Service.
kubectl get service frontend
The response should be similar to this:
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
frontend LoadBalancer 10.51.242.136 109.197.92.229 80:32372/TCP 1m
Copy the external IP address, and load the page in your browser to view your guestbook.
Note: Try adding some guestbook entries by typing in a message, and clicking Submit.
The message you typed appears in the frontend. This message indicates that
data is successfully added to Redis through the Services you created earlier.
Scale the Web Frontend
You can scale up or down as needed because your servers are defined as a
Service that uses a Deployment controller.
Run the following command to scale up the number of frontend Pods:
kubectl scale deployment frontend --replicas=5
Query the list of Pods to verify the number of frontend Pods running:
This tutorial provides an introduction to managing applications with
StatefulSets.
It demonstrates how to create, delete, scale, and update the Pods of StatefulSets.
Before you begin
Before you begin this tutorial, you should familiarize yourself with the
following Kubernetes concepts:
Note: This tutorial assumes that your cluster is configured to dynamically provision
PersistentVolumes. If your cluster is not configured to do so, you
will have to manually provision two 1 GiB volumes prior to starting this
tutorial.
Objectives
StatefulSets are intended to be used with stateful applications and distributed
systems. However, the administration of stateful applications and
distributed systems on Kubernetes is a broad, complex topic. In order to
demonstrate the basic features of a StatefulSet, and not to conflate the former
topic with the latter, you will deploy a simple web application using a StatefulSet.
After this tutorial, you will be familiar with the following.
How to create a StatefulSet
How a StatefulSet manages its Pods
How to delete a StatefulSet
How to scale a StatefulSet
How to update a StatefulSet's Pods
Creating a StatefulSet
Begin by creating a StatefulSet using the example below. It is similar to the
example presented in the
StatefulSets concept.
It creates a headless Service,
nginx, to publish the IP addresses of Pods in the StatefulSet, web.
Download the example above, and save it to a file named web.yaml
You will need to use two terminal windows. In the first terminal, use
kubectl get to watch the creation
of the StatefulSet's Pods.
kubectl get pods -w -l app=nginx
In the second terminal, use
kubectl apply to create the
headless Service and StatefulSet defined in web.yaml.
kubectl apply -f web.yaml
service/nginx created
statefulset.apps/web created
The command above creates two Pods, each running an
NGINX webserver. Get the nginx Service...
kubectl get service nginx
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
nginx ClusterIP None <none> 80/TCP 12s
...then get the web StatefulSet, to verify that both were created successfully:
kubectl get statefulset web
NAME DESIRED CURRENT AGE
web 2 1 20s
Ordered Pod Creation
For a StatefulSet with n replicas, when Pods are being deployed, they are
created sequentially, ordered from {0..n-1}. Examine the output of the
kubectl get command in the first terminal. Eventually, the output will
look like the example below.
Notice that the web-1 Pod is not launched until the web-0 Pod is
Running (see Pod Phase)
and Ready (see type in Pod Conditions).
Pods in a StatefulSet
Pods in a StatefulSet have a unique ordinal index and a stable network identity.
Examining the Pod's Ordinal Index
Get the StatefulSet's Pods:
kubectl get pods -l app=nginx
NAME READY STATUS RESTARTS AGE
web-0 1/1 Running 0 1m
web-1 1/1 Running 0 1m
As mentioned in the StatefulSets
concept, the Pods in a StatefulSet have a sticky, unique identity. This identity
is based on a unique ordinal index that is assigned to each Pod by the
StatefulSet controller.
The Pods' names take the form <statefulset name>-<ordinal index>.
Since the web StatefulSet has two replicas, it creates two Pods, web-0 and web-1.
Using Stable Network Identities
Each Pod has a stable hostname based on its ordinal index. Use
kubectl exec to execute the
hostname command in each Pod:
for i in 0 1; do kubectl exec"web-$i" -- sh -c 'hostname'; done
web-0
web-1
Use kubectl run to execute
a container that provides the nslookup command from the dnsutils package.
Using nslookup on the Pods' hostnames, you can examine their in-cluster DNS
addresses:
kubectl run -i --tty --image busybox:1.28 dns-test --restart=Never --rm
which starts a new shell. In that new shell, run:
# Run this in the dns-test container shellnslookup web-0.nginx
The CNAME of the headless service points to SRV records (one for each Pod that
is Running and Ready). The SRV records point to A record entries that
contain the Pods' IP addresses.
In one terminal, watch the StatefulSet's Pods:
kubectl get pod -w -l app=nginx
In a second terminal, use
kubectl delete to delete all
the Pods in the StatefulSet:
kubectl delete pod -l app=nginx
pod "web-0" deleted
pod "web-1" deleted
Wait for the StatefulSet to restart them, and for both Pods to transition to
Running and Ready:
kubectl get pod -w -l app=nginx
NAME READY STATUS RESTARTS AGE
web-0 0/1 ContainerCreating 0 0s
NAME READY STATUS RESTARTS AGE
web-0 1/1 Running 0 2s
web-1 0/1 Pending 0 0s
web-1 0/1 Pending 0 0s
web-1 0/1 ContainerCreating 0 0s
web-1 1/1 Running 0 34s
Use kubectl exec and kubectl run to view the Pods' hostnames and in-cluster
DNS entries. First, view the Pods' hostnames:
for i in 0 1; do kubectl exec web-$i -- sh -c 'hostname'; done
web-0
web-1
then, run:
kubectl run -i --tty --image busybox:1.28 dns-test --restart=Never --rm /bin/sh
which starts a new shell.
In that new shell, run:
# Run this in the dns-test container shellnslookup web-0.nginx
The Pods' ordinals, hostnames, SRV records, and A record names have not changed,
but the IP addresses associated with the Pods may have changed. In the cluster
used for this tutorial, they have. This is why it is important not to configure
other applications to connect to Pods in a StatefulSet by IP address.
If you need to find and connect to the active members of a StatefulSet, you
should query the CNAME of the headless Service
(nginx.default.svc.cluster.local). The SRV records associated with the
CNAME will contain only the Pods in the StatefulSet that are Running and
Ready.
If your application already implements connection logic that tests for
liveness and readiness, you can use the SRV records of the Pods (
web-0.nginx.default.svc.cluster.local,
web-1.nginx.default.svc.cluster.local), as they are stable, and your
application will be able to discover the Pods' addresses when they transition
to Running and Ready.
Writing to Stable Storage
Get the PersistentVolumeClaims for web-0 and web-1:
kubectl get pvc -l app=nginx
The output is similar to:
NAME STATUS VOLUME CAPACITY ACCESSMODES AGE
www-web-0 Bound pvc-15c268c7-b507-11e6-932f-42010a800002 1Gi RWO 48s
www-web-1 Bound pvc-15c79307-b507-11e6-932f-42010a800002 1Gi RWO 48s
As the cluster used in this tutorial is configured to dynamically provision PersistentVolumes,
the PersistentVolumes were created and bound automatically.
The NGINX webserver, by default, serves an index file from
/usr/share/nginx/html/index.html. The volumeMounts field in the
StatefulSet's spec ensures that the /usr/share/nginx/html directory is
backed by a PersistentVolume.
Write the Pods' hostnames to their index.html files and verify that the NGINX
webservers serve the hostnames:
for i in 0 1; do kubectl exec"web-$i" -- sh -c 'echo "$(hostname)" > /usr/share/nginx/html/index.html'; donefor i in 0 1; do kubectl exec -i -t "web-$i" -- curl http://localhost/; done
web-0
web-1
Note:
If you instead see 403 Forbidden responses for the above curl command,
you will need to fix the permissions of the directory mounted by the volumeMounts
(due to a bug when using hostPath volumes),
by running:
for i in 0 1; do kubectl exec web-$i -- chmod 755 /usr/share/nginx/html; done
before retrying the curl command above.
In one terminal, watch the StatefulSet's Pods:
kubectl get pod -w -l app=nginx
In a second terminal, delete all of the StatefulSet's Pods:
kubectl delete pod -l app=nginx
pod "web-0" deleted
pod "web-1" deleted
Examine the output of the kubectl get command in the first terminal, and wait
for all of the Pods to transition to Running and Ready.
kubectl get pod -w -l app=nginx
NAME READY STATUS RESTARTS AGE
web-0 0/1 ContainerCreating 0 0s
NAME READY STATUS RESTARTS AGE
web-0 1/1 Running 0 2s
web-1 0/1 Pending 0 0s
web-1 0/1 Pending 0 0s
web-1 0/1 ContainerCreating 0 0s
web-1 1/1 Running 0 34s
Verify the web servers continue to serve their hostnames:
for i in 0 1; do kubectl exec -i -t "web-$i" -- curl http://localhost/; done
web-0
web-1
Even though web-0 and web-1 were rescheduled, they continue to serve their
hostnames because the PersistentVolumes associated with their
PersistentVolumeClaims are remounted to their volumeMounts. No matter what
node web-0and web-1 are scheduled on, their PersistentVolumes will be
mounted to the appropriate mount points.
Scaling a StatefulSet
Scaling a StatefulSet refers to increasing or decreasing the number of replicas.
This is accomplished by updating the replicas field. You can use either
kubectl scale or
kubectl patch to scale a StatefulSet.
Scaling Up
In one terminal window, watch the Pods in the StatefulSet:
kubectl get pods -w -l app=nginx
In another terminal window, use kubectl scale to scale the number of replicas
to 5:
kubectl scale sts web --replicas=5
statefulset.apps/web scaled
Examine the output of the kubectl get command in the first terminal, and wait
for the three additional Pods to transition to Running and Ready.
The StatefulSet controller scaled the number of replicas. As with
StatefulSet creation, the StatefulSet controller
created each Pod sequentially with respect to its ordinal index, and it
waited for each Pod's predecessor to be Running and Ready before launching the
subsequent Pod.
Scaling Down
In one terminal, watch the StatefulSet's Pods:
kubectl get pods -w -l app=nginx
In another terminal, use kubectl patch to scale the StatefulSet back down to
three replicas:
kubectl patch sts web -p '{"spec":{"replicas":3}}'
statefulset.apps/web patched
Wait for web-4 and web-3 to transition to Terminating.
kubectl get pods -w -l app=nginx
NAME READY STATUS RESTARTS AGE
web-0 1/1 Running 0 3h
web-1 1/1 Running 0 3h
web-2 1/1 Running 0 55s
web-3 1/1 Running 0 36s
web-4 0/1 ContainerCreating 0 18s
NAME READY STATUS RESTARTS AGE
web-4 1/1 Running 0 19s
web-4 1/1 Terminating 0 24s
web-4 1/1 Terminating 0 24s
web-3 1/1 Terminating 0 42s
web-3 1/1 Terminating 0 42s
Ordered Pod Termination
The controller deleted one Pod at a time, in reverse order with respect to its
ordinal index, and it waited for each to be completely shutdown before
deleting the next.
There are still five PersistentVolumeClaims and five PersistentVolumes.
When exploring a Pod's stable storage, we saw that the PersistentVolumes mounted to the Pods of a StatefulSet are not deleted when the StatefulSet's Pods are deleted. This is still true when Pod deletion is caused by scaling the StatefulSet down.
Updating StatefulSets
In Kubernetes 1.7 and later, the StatefulSet controller supports automated updates. The
strategy used is determined by the spec.updateStrategy field of the
StatefulSet API Object. This feature can be used to upgrade the container
images, resource requests and/or limits, labels, and annotations of the Pods in a
StatefulSet. There are two valid update strategies, RollingUpdate and
OnDelete.
RollingUpdate update strategy is the default for StatefulSets.
Rolling Update
The RollingUpdate update strategy will update all Pods in a StatefulSet, in
reverse ordinal order, while respecting the StatefulSet guarantees.
Patch the web StatefulSet to apply the RollingUpdate update strategy:
kubectl patch statefulset web -p '{"spec":{"updateStrategy":{"type":"RollingUpdate"}}}'
statefulset.apps/web patched
In one terminal window, patch the web StatefulSet to change the container
image again:
kubectl patch statefulset web --type='json' -p='[{"op": "replace", "path": "/spec/template/spec/containers/0/image", "value":"gcr.io/google_containers/nginx-slim:0.8"}]'
statefulset.apps/web patched
In another terminal, watch the Pods in the StatefulSet:
The Pods in the StatefulSet are updated in reverse ordinal order. The
StatefulSet controller terminates each Pod, and waits for it to transition to Running and
Ready prior to updating the next Pod. Note that, even though the StatefulSet
controller will not proceed to update the next Pod until its ordinal successor
is Running and Ready, it will restore any Pod that fails during the update to
its current version.
Pods that have already received the update will be restored to the updated version,
and Pods that have not yet received the update will be restored to the previous
version. In this way, the controller attempts to continue to keep the application
healthy and the update consistent in the presence of intermittent failures.
Get the Pods to view their container images:
for p in 01 2; do kubectl get pod "web-$p" --template '{{range $i, $c := .spec.containers}}{{$c.image}}{{end}}'; echo; done
All the Pods in the StatefulSet are now running the previous container image.
Note: You can also use kubectl rollout status sts/<name> to view
the status of a rolling update to a StatefulSet
Staging an Update
You can stage an update to a StatefulSet by using the partition parameter of
the RollingUpdate update strategy. A staged update will keep all of the Pods
in the StatefulSet at the current version while allowing mutations to the
StatefulSet's .spec.template.
Patch the web StatefulSet to add a partition to the updateStrategy field:
kubectl patch statefulset web -p '{"spec":{"updateStrategy":{"type":"RollingUpdate","rollingUpdate":{"partition":3}}}}'
statefulset.apps/web patched
Patch the StatefulSet again to change the container's image:
kubectl patch statefulset web --type='json' -p='[{"op": "replace", "path": "/spec/template/spec/containers/0/image", "value":"registry.k8s.io/nginx-slim:0.7"}]'
statefulset.apps/web patched
Delete a Pod in the StatefulSet:
kubectl delete pod web-2
pod "web-2" deleted
Wait for the Pod to be Running and Ready.
kubectl get pod -l app=nginx -w
NAME READY STATUS RESTARTS AGE
web-0 1/1 Running 0 4m
web-1 1/1 Running 0 4m
web-2 0/1 ContainerCreating 0 11s
web-2 1/1 Running 0 18s
Get the Pod's container image:
kubectl get pod web-2 --template '{{range $i, $c := .spec.containers}}{{$c.image}}{{end}}'
registry.k8s.io/nginx-slim:0.8
Notice that, even though the update strategy is RollingUpdate the StatefulSet
restored the Pod with its original container. This is because the
ordinal of the Pod is less than the partition specified by the
updateStrategy.
Rolling Out a Canary
You can roll out a canary to test a modification by decrementing the partition
you specified above.
Patch the StatefulSet to decrement the partition:
kubectl patch statefulset web -p '{"spec":{"updateStrategy":{"type":"RollingUpdate","rollingUpdate":{"partition":2}}}}'
statefulset.apps/web patched
Wait for web-2 to be Running and Ready.
kubectl get pod -l app=nginx -w
NAME READY STATUS RESTARTS AGE
web-0 1/1 Running 0 4m
web-1 1/1 Running 0 4m
web-2 0/1 ContainerCreating 0 11s
web-2 1/1 Running 0 18s
Get the Pod's container:
kubectl get pod web-2 --template '{{range $i, $c := .spec.containers}}{{$c.image}}{{end}}'
registry.k8s.io/nginx-slim:0.7
When you changed the partition, the StatefulSet controller automatically
updated the web-2 Pod because the Pod's ordinal was greater than or equal to
the partition.
kubectl get pod web-1 --template '{{range $i, $c := .spec.containers}}{{$c.image}}{{end}}'
registry.k8s.io/nginx-slim:0.8
web-1 was restored to its original configuration because the Pod's ordinal
was less than the partition. When a partition is specified, all Pods with an
ordinal that is greater than or equal to the partition will be updated when the
StatefulSet's .spec.template is updated. If a Pod that has an ordinal less
than the partition is deleted or otherwise terminated, it will be restored to
its original configuration.
Phased Roll Outs
You can perform a phased roll out (e.g. a linear, geometric, or exponential
roll out) using a partitioned rolling update in a similar manner to how you
rolled out a canary. To perform a phased roll out, set
the partition to the ordinal at which you want the controller to pause the
update.
The partition is currently set to 2. Set the partition to 0:
kubectl patch statefulset web -p '{"spec":{"updateStrategy":{"type":"RollingUpdate","rollingUpdate":{"partition":0}}}}'
statefulset.apps/web patched
Wait for all of the Pods in the StatefulSet to become Running and Ready.
By moving the partition to 0, you allowed the StatefulSet to
continue the update process.
On Delete
The OnDelete update strategy implements the legacy (1.6 and prior) behavior,
When you select this update strategy, the StatefulSet controller will not
automatically update Pods when a modification is made to the StatefulSet's
.spec.template field. This strategy can be selected by setting the
.spec.template.updateStrategy.type to OnDelete.
Deleting StatefulSets
StatefulSet supports both Non-Cascading and Cascading deletion. In a
Non-Cascading Delete, the StatefulSet's Pods are not deleted when the StatefulSet is deleted. In a Cascading Delete, both the StatefulSet and its Pods are
deleted.
Non-Cascading Delete
In one terminal window, watch the Pods in the StatefulSet.
kubectl get pods -w -l app=nginx
Use kubectl delete to delete the
StatefulSet. Make sure to supply the --cascade=orphan parameter to the
command. This parameter tells Kubernetes to only delete the StatefulSet, and to
not delete any of its Pods.
kubectl delete statefulset web --cascade=orphan
statefulset.apps "web" deleted
Get the Pods, to examine their status:
kubectl get pods -l app=nginx
NAME READY STATUS RESTARTS AGE
web-0 1/1 Running 0 6m
web-1 1/1 Running 0 7m
web-2 1/1 Running 0 5m
Even though web has been deleted, all of the Pods are still Running and Ready.
Delete web-0:
kubectl delete pod web-0
pod "web-0" deleted
Get the StatefulSet's Pods:
kubectl get pods -l app=nginx
NAME READY STATUS RESTARTS AGE
web-1 1/1 Running 0 10m
web-2 1/1 Running 0 7m
As the web StatefulSet has been deleted, web-0 has not been relaunched.
In one terminal, watch the StatefulSet's Pods.
kubectl get pods -w -l app=nginx
In a second terminal, recreate the StatefulSet. Note that, unless
you deleted the nginx Service (which you should not have), you will see
an error indicating that the Service already exists.
kubectl apply -f web.yaml
statefulset.apps/web created
service/nginx unchanged
Ignore the error. It only indicates that an attempt was made to create the nginx
headless Service even though that Service already exists.
Examine the output of the kubectl get command running in the first terminal.
kubectl get pods -w -l app=nginx
NAME READY STATUS RESTARTS AGE
web-1 1/1 Running 0 16m
web-2 1/1 Running 0 2m
NAME READY STATUS RESTARTS AGE
web-0 0/1 Pending 0 0s
web-0 0/1 Pending 0 0s
web-0 0/1 ContainerCreating 0 0s
web-0 1/1 Running 0 18s
web-2 1/1 Terminating 0 3m
web-2 0/1 Terminating 0 3m
web-2 0/1 Terminating 0 3m
web-2 0/1 Terminating 0 3m
When the web StatefulSet was recreated, it first relaunched web-0.
Since web-1 was already Running and Ready, when web-0 transitioned to
Running and Ready, it adopted this Pod. Since you recreated the StatefulSet
with replicas equal to 2, once web-0 had been recreated, and once
web-1 had been determined to already be Running and Ready, web-2 was
terminated.
Let's take another look at the contents of the index.html file served by the
Pods' webservers:
for i in 0 1; do kubectl exec -i -t "web-$i" -- curl http://localhost/; done
web-0
web-1
Even though you deleted both the StatefulSet and the web-0 Pod, it still
serves the hostname originally entered into its index.html file. This is
because the StatefulSet never deletes the PersistentVolumes associated with a
Pod. When you recreated the StatefulSet and it relaunched web-0, its original
PersistentVolume was remounted.
Cascading Delete
In one terminal window, watch the Pods in the StatefulSet.
kubectl get pods -w -l app=nginx
In another terminal, delete the StatefulSet again. This time, omit the
--cascade=orphan parameter.
kubectl delete statefulset web
statefulset.apps "web" deleted
Examine the output of the kubectl get command running in the first terminal,
and wait for all of the Pods to transition to Terminating.
kubectl get pods -w -l app=nginx
NAME READY STATUS RESTARTS AGE
web-0 1/1 Running 0 11m
web-1 1/1 Running 0 27m
NAME READY STATUS RESTARTS AGE
web-0 1/1 Terminating 0 12m
web-1 1/1 Terminating 0 29m
web-0 0/1 Terminating 0 12m
web-0 0/1 Terminating 0 12m
web-0 0/1 Terminating 0 12m
web-1 0/1 Terminating 0 29m
web-1 0/1 Terminating 0 29m
web-1 0/1 Terminating 0 29m
As you saw in the Scaling Down section, the Pods
are terminated one at a time, with respect to the reverse order of their ordinal
indices. Before terminating a Pod, the StatefulSet controller waits for
the Pod's successor to be completely terminated.
Note: Although a cascading delete removes a StatefulSet together with its Pods,
the cascade does not delete the headless Service associated with the StatefulSet.
You must delete the nginx Service manually.
kubectl delete service nginx
service "nginx" deleted
Recreate the StatefulSet and headless Service one more time:
kubectl apply -f web.yaml
service/nginx created
statefulset.apps/web created
When all of the StatefulSet's Pods transition to Running and Ready, retrieve
the contents of their index.html files:
for i in 0 1; do kubectl exec -i -t "web-$i" -- curl http://localhost/; done
web-0
web-1
Even though you completely deleted the StatefulSet, and all of its Pods, the
Pods are recreated with their PersistentVolumes mounted, and web-0 and
web-1 continue to serve their hostnames.
Finally, delete the nginx Service...
kubectl delete service nginx
service "nginx" deleted
...and the web StatefulSet:
kubectl delete statefulset web
statefulset "web" deleted
Pod Management Policy
For some distributed systems, the StatefulSet ordering guarantees are
unnecessary and/or undesirable. These systems require only uniqueness and
identity. To address this, in Kubernetes 1.7, we introduced
.spec.podManagementPolicy to the StatefulSet API Object.
OrderedReady Pod Management
OrderedReady pod management is the default for StatefulSets. It tells the
StatefulSet controller to respect the ordering guarantees demonstrated
above.
Parallel Pod Management
Parallel pod management tells the StatefulSet controller to launch or
terminate all Pods in parallel, and not to wait for Pods to become Running
and Ready or completely terminated prior to launching or terminating another
Pod. This option only affects the behavior for scaling operations. Updates are not affected.
Note: You also need to delete the persistent storage media for the PersistentVolumes
used in this tutorial.
Follow the necessary steps, based on your environment, storage configuration,
and provisioning method, to ensure that all storage is reclaimed.
6.2 - Example: Deploying WordPress and MySQL with Persistent Volumes
This tutorial shows you how to deploy a WordPress site and a MySQL database using Minikube. Both applications use PersistentVolumes and PersistentVolumeClaims to store data.
A PersistentVolume (PV) is a piece of storage in the cluster that has been manually provisioned by an administrator, or dynamically provisioned by Kubernetes using a StorageClass. A PersistentVolumeClaim (PVC) is a request for storage by a user that can be fulfilled by a PV. PersistentVolumes and PersistentVolumeClaims are independent from Pod lifecycles and preserve data through restarting, rescheduling, and even deleting Pods.
Warning: This deployment is not suitable for production use cases, as it uses single instance WordPress and MySQL Pods. Consider using WordPress Helm Chart to deploy WordPress in production.
Note: The files provided in this tutorial are using GA Deployment APIs and are specific to kubernetes version 1.9 and later. If you wish to use this tutorial with an earlier version of Kubernetes, please update the API version appropriately, or reference earlier versions of this tutorial.
Objectives
Create PersistentVolumeClaims and PersistentVolumes
Create a kustomization.yaml with
a Secret generator
MySQL resource configs
WordPress resource configs
Apply the kustomization directory by kubectl apply -k ./
Clean up
Before you begin
You need to have a Kubernetes cluster, and the kubectl command-line tool must
be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a
cluster, you can create one by using
minikube
or you can use one of these Kubernetes playgrounds:
Create PersistentVolumeClaims and PersistentVolumes
MySQL and Wordpress each require a PersistentVolume to store data. Their PersistentVolumeClaims will be created at the deployment step.
Many cluster environments have a default StorageClass installed. When a StorageClass is not specified in the PersistentVolumeClaim, the cluster's default StorageClass is used instead.
When a PersistentVolumeClaim is created, a PersistentVolume is dynamically provisioned based on the StorageClass configuration.
Warning: In local clusters, the default StorageClass uses the hostPath provisioner. hostPath volumes are only suitable for development and testing. With hostPath volumes, your data lives in /tmp on the node the Pod is scheduled onto and does not move between nodes. If a Pod dies and gets scheduled to another node in the cluster, or the node is rebooted, the data is lost.
Note: If you are bringing up a cluster that needs to use the hostPath provisioner, the --enable-hostpath-provisioner flag must be set in the controller-manager component.
Note: If you have a Kubernetes cluster running on Google Kubernetes Engine, please follow this guide.
Create a kustomization.yaml
Add a Secret generator
A Secret is an object that stores a piece of sensitive data like a password or key. Since 1.14, kubectl supports the management of Kubernetes objects using a kustomization file. You can create a Secret by generators in kustomization.yaml.
Add a Secret generator in kustomization.yaml from the following command. You will need to replace YOUR_PASSWORD with the password you want to use.
The following manifest describes a single-instance MySQL Deployment. The MySQL container mounts the PersistentVolume at /var/lib/mysql. The MYSQL_ROOT_PASSWORD environment variable sets the database password from the Secret.
The following manifest describes a single-instance WordPress Deployment. The WordPress container mounts the
PersistentVolume at /var/www/html for website data files. The WORDPRESS_DB_HOST environment variable sets
the name of the MySQL Service defined above, and WordPress will access the database by Service. The
WORDPRESS_DB_PASSWORD environment variable sets the database password from the Secret kustomize generated.
The kustomization.yaml contains all the resources for deploying a WordPress site and a
MySQL database. You can apply the directory by
kubectl apply -k ./
Now you can verify that all objects exist.
Verify that the Secret exists by running the following command:
kubectl get secrets
The response should be like this:
NAME TYPE DATA AGE
mysql-pass-c57bb4t7mf Opaque 1 9s
Verify that a PersistentVolume got dynamically provisioned.
kubectl get pvc
Note: It can take up to a few minutes for the PVs to be provisioned and bound.
The response should be like this:
NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE
mysql-pv-claim Bound pvc-8cbd7b2e-4044-11e9-b2bb-42010a800002 20Gi RWO standard 77s
wp-pv-claim Bound pvc-8cd0df54-4044-11e9-b2bb-42010a800002 20Gi RWO standard 77s
Verify that the Pod is running by running the following command:
kubectl get pods
Note: It can take up to a few minutes for the Pod's Status to be RUNNING.
The response should be like this:
NAME READY STATUS RESTARTS AGE
wordpress-mysql-1894417608-x5dzt 1/1 Running 0 40s
Verify that the Service is running by running the following command:
kubectl get services wordpress
The response should be like this:
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
wordpress LoadBalancer 10.0.0.89 <pending> 80:32406/TCP 4m
Note: Minikube can only expose Services through NodePort. The EXTERNAL-IP is always pending.
Run the following command to get the IP Address for the WordPress Service:
minikube service wordpress --url
The response should be like this:
http://1.2.3.4:32406
Copy the IP address, and load the page in your browser to view your site.
You should see the WordPress set up page similar to the following screenshot.
Warning: Do not leave your WordPress installation on this page. If another user finds it, they can set up a website on your instance and use it to serve malicious content.
Either install WordPress by creating a username and password or delete your instance.
Cleaning up
Run the following command to delete your Secret, Deployments, Services and PersistentVolumeClaims:
6.3 - Example: Deploying Cassandra with a StatefulSet
This tutorial shows you how to run Apache Cassandra on Kubernetes.
Cassandra, a database, needs persistent storage to provide data durability (application state).
In this example, a custom Cassandra seed provider lets the database discover new Cassandra instances as they join the Cassandra cluster.
StatefulSets make it easier to deploy stateful applications into your Kubernetes cluster.
For more information on the features used in this tutorial, see
StatefulSet.
Note:
Cassandra and Kubernetes both use the term node to mean a member of a cluster. In this
tutorial, the Pods that belong to the StatefulSet are Cassandra nodes and are members
of the Cassandra cluster (called a ring). When those Pods run in your Kubernetes cluster,
the Kubernetes control plane schedules those Pods onto Kubernetes
Nodes.
When a Cassandra node starts, it uses a seed list to bootstrap discovery of other
nodes in the ring.
This tutorial deploys a custom Cassandra seed provider that lets the database discover
new Cassandra Pods as they appear inside your Kubernetes cluster.
You need to have a Kubernetes cluster, and the kubectl command-line tool must
be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a
cluster, you can create one by using
minikube
or you can use one of these Kubernetes playgrounds:
To complete this tutorial, you should already have a basic familiarity with
Pods,
Services, and
StatefulSets.
Additional Minikube setup instructions
Caution:
Minikube defaults to 2048MB of memory and 2 CPU.
Running Minikube with the default resource configuration results in insufficient resource
errors during this tutorial. To avoid these errors, start Minikube with the following settings:
minikube start --memory 5120 --cpus=4
Creating a headless Service for Cassandra
In Kubernetes, a Service describes a set of
Pods that perform the same task.
The following Service is used for DNS lookups between Cassandra Pods and clients within your cluster:
apiVersion:apps/v1kind:StatefulSetmetadata:name:cassandralabels:app:cassandraspec:serviceName:cassandrareplicas:3selector:matchLabels:app:cassandratemplate:metadata:labels:app:cassandraspec:terminationGracePeriodSeconds:1800containers:- name:cassandraimage:gcr.io/google-samples/cassandra:v13imagePullPolicy:Alwaysports:- containerPort:7000name:intra-node- containerPort:7001name:tls-intra-node- containerPort:7199name:jmx- containerPort:9042name:cqlresources:limits:cpu:"500m"memory:1Girequests:cpu:"500m"memory:1GisecurityContext:capabilities:add:- IPC_LOCKlifecycle:preStop:exec:command:- /bin/sh- -c- nodetool drainenv:- name:MAX_HEAP_SIZEvalue:512M- name:HEAP_NEWSIZEvalue:100M- name:CASSANDRA_SEEDSvalue:"cassandra-0.cassandra.default.svc.cluster.local"- name:CASSANDRA_CLUSTER_NAMEvalue:"K8Demo"- name:CASSANDRA_DCvalue:"DC1-K8Demo"- name:CASSANDRA_RACKvalue:"Rack1-K8Demo"- name:POD_IPvalueFrom:fieldRef:fieldPath:status.podIPreadinessProbe:exec:command:- /bin/bash- -c- /ready-probe.shinitialDelaySeconds:15timeoutSeconds:5# These volume mounts are persistent. They are like inline claims,# but not exactly because the names need to match exactly one of# the stateful pod volumes.volumeMounts:- name:cassandra-datamountPath:/cassandra_data# These are converted to volume claims by the controller# and mounted at the paths mentioned above.# do not use these in production until ssd GCEPersistentDisk or other ssd pdvolumeClaimTemplates:- metadata:name:cassandra-dataspec:accessModes:["ReadWriteOnce"]storageClassName:fastresources:requests:storage:1Gi---kind:StorageClassapiVersion:storage.k8s.io/v1metadata:name:fastprovisioner:k8s.io/minikube-hostpathparameters:type:pd-ssd
Create the Cassandra StatefulSet from the cassandra-statefulset.yaml file:
# Use this if you are able to apply cassandra-statefulset.yaml unmodifiedkubectl apply -f https://k8s.io/examples/application/cassandra/cassandra-statefulset.yaml
# Use this if you needed to modify cassandra-statefulset.yaml locallykubectl apply -f cassandra-statefulset.yaml
Validating the Cassandra StatefulSet
Get the Cassandra StatefulSet:
kubectl get statefulset cassandra
The response should be similar to:
NAME DESIRED CURRENT AGE
cassandra 3 0 13s
The StatefulSet resource deploys Pods sequentially.
Get the Pods to see the ordered creation status:
kubectl get pods -l="app=cassandra"
The response should be similar to:
NAME READY STATUS RESTARTS AGE
cassandra-0 1/1 Running 0 1m
cassandra-1 0/1 ContainerCreating 0 8s
It can take several minutes for all three Pods to deploy. Once they are deployed, the same command
returns output similar to:
NAME READY STATUS RESTARTS AGE
cassandra-0 1/1 Running 0 10m
cassandra-1 1/1 Running 0 9m
cassandra-2 1/1 Running 0 8m
Run the Cassandra nodetool inside the first Pod, to
display the status of the ring.
kubectl exec -it cassandra-0 -- nodetool status
The response should look something like:
Datacenter: DC1-K8Demo
======================
Status=Up/Down
|/ State=Normal/Leaving/Joining/Moving
-- Address Load Tokens Owns (effective) Host ID Rack
UN 172.17.0.5 83.57 KiB 32 74.0% e2dd09e6-d9d3-477e-96c5-45094c08db0f Rack1-K8Demo
UN 172.17.0.4 101.04 KiB 32 58.8% f89d6835-3a42-4419-92b3-0e62cae1479c Rack1-K8Demo
UN 172.17.0.6 84.74 KiB 32 67.1% a6a1e8c2-3dc5-4417-b1a0-26507af2aaad Rack1-K8Demo
Modifying the Cassandra StatefulSet
Use kubectl edit to modify the size of a Cassandra StatefulSet.
Run the following command:
kubectl edit statefulset cassandra
This command opens an editor in your terminal. The line you need to change is the replicas field.
The following sample is an excerpt of the StatefulSet file:
# Please edit the object below. Lines beginning with a '#' will be ignored,# and an empty file will abort the edit. If an error occurs while saving this file will be# reopened with the relevant failures.#apiVersion:apps/v1kind:StatefulSetmetadata:creationTimestamp:2016-08-13T18:40:58Zgeneration:1labels:app:cassandraname:cassandranamespace:defaultresourceVersion:"323"uid:7a219483-6185-11e6-a910-42010a8a0fc0spec:replicas:3
Change the number of replicas to 4, and then save the manifest.
The StatefulSet now scales to run with 4 Pods.
Get the Cassandra StatefulSet to verify your change:
kubectl get statefulset cassandra
The response should be similar to:
NAME DESIRED CURRENT AGE
cassandra 4 4 36m
Cleaning up
Deleting or scaling a StatefulSet down does not delete the volumes associated with the StatefulSet.
This setting is for your safety because your data is more valuable than automatically purging all related StatefulSet resources.
Warning: Depending on the storage class and reclaim policy, deleting the PersistentVolumeClaims may cause the associated volumes
to also be deleted. Never assume you'll be able to access data if its volume claims are deleted.
Run the following commands (chained together into a single command) to delete everything in the Cassandra StatefulSet:
This image includes a standard Cassandra installation from the Apache Debian repo.
By using environment variables you can change values that are inserted into cassandra.yaml.
You must have a cluster with at least four nodes, and each node requires at least 2 CPUs and 4 GiB of memory. In this tutorial you will cordon and drain the cluster's nodes. This means that the cluster will terminate and evict all Pods on its nodes, and the nodes will temporarily become unschedulable. You should use a dedicated cluster for this tutorial, or you should ensure that the disruption you cause will not interfere with other tenants.
This tutorial assumes that you have configured your cluster to dynamically provision
PersistentVolumes. If your cluster is not configured to do so, you
will have to manually provision three 20 GiB volumes before starting this
tutorial.
Objectives
After this tutorial, you will know the following.
How to deploy a ZooKeeper ensemble using StatefulSet.
How to consistently configure the ensemble.
How to spread the deployment of ZooKeeper servers in the ensemble.
How to use PodDisruptionBudgets to ensure service availability during planned maintenance.
ZooKeeper
Apache ZooKeeper is a
distributed, open-source coordination service for distributed applications.
ZooKeeper allows you to read, write, and observe updates to data. Data are
organized in a file system like hierarchy and replicated to all ZooKeeper
servers in the ensemble (a set of ZooKeeper servers). All operations on data
are atomic and sequentially consistent. ZooKeeper ensures this by using the
Zab
consensus protocol to replicate a state machine across all servers in the ensemble.
The ensemble uses the Zab protocol to elect a leader, and the ensemble cannot write data until that election is complete. Once complete, the ensemble uses Zab to ensure that it replicates all writes to a quorum before it acknowledges and makes them visible to clients. Without respect to weighted quorums, a quorum is a majority component of the ensemble containing the current leader. For instance, if the ensemble has three servers, a component that contains the leader and one other server constitutes a quorum. If the ensemble can not achieve a quorum, the ensemble cannot write data.
ZooKeeper servers keep their entire state machine in memory, and write every mutation to a durable WAL (Write Ahead Log) on storage media. When a server crashes, it can recover its previous state by replaying the WAL. To prevent the WAL from growing without bound, ZooKeeper servers will periodically snapshot them in memory state to storage media. These snapshots can be loaded directly into memory, and all WAL entries that preceded the snapshot may be discarded.
The StatefulSet controller creates three Pods, and each Pod has a container with
a ZooKeeper server.
Facilitating leader election
Because there is no terminating algorithm for electing a leader in an anonymous network, Zab requires explicit membership configuration to perform leader election. Each server in the ensemble needs to have a unique identifier, all servers need to know the global set of identifiers, and each identifier needs to be associated with a network address.
Use kubectl exec to get the hostnames
of the Pods in the zk StatefulSet.
for i in 01 2; do kubectl exec zk-$i -- hostname; done
The StatefulSet controller provides each Pod with a unique hostname based on its ordinal index. The hostnames take the form of <statefulset name>-<ordinal index>. Because the replicas field of the zk StatefulSet is set to 3, the Set's controller creates three Pods with their hostnames set to zk-0, zk-1, and
zk-2.
zk-0
zk-1
zk-2
The servers in a ZooKeeper ensemble use natural numbers as unique identifiers, and store each server's identifier in a file called myid in the server's data directory.
To examine the contents of the myid file for each server use the following command.
for i in 01 2; doecho"myid zk-$i";kubectl exec zk-$i -- cat /var/lib/zookeeper/data/myid; done
Because the identifiers are natural numbers and the ordinal indices are non-negative integers, you can generate an identifier by adding 1 to the ordinal.
myid zk-0
1
myid zk-1
2
myid zk-2
3
To get the Fully Qualified Domain Name (FQDN) of each Pod in the zk StatefulSet use the following command.
for i in 01 2; do kubectl exec zk-$i -- hostname -f; done
The zk-hs Service creates a domain for all of the Pods,
zk-hs.default.svc.cluster.local.
The A records in Kubernetes DNS resolve the FQDNs to the Pods' IP addresses. If Kubernetes reschedules the Pods, it will update the A records with the Pods' new IP addresses, but the A records names will not change.
ZooKeeper stores its application configuration in a file named zoo.cfg. Use kubectl exec to view the contents of the zoo.cfg file in the zk-0 Pod.
In the server.1, server.2, and server.3 properties at the bottom of
the file, the 1, 2, and 3 correspond to the identifiers in the
ZooKeeper servers' myid files. They are set to the FQDNs for the Pods in
the zk StatefulSet.
Consensus protocols require that the identifiers of each participant be unique. No two participants in the Zab protocol should claim the same unique identifier. This is necessary to allow the processes in the system to agree on which processes have committed which data. If two Pods are launched with the same ordinal, two ZooKeeper servers would both identify themselves as the same server.
The A records for each Pod are entered when the Pod becomes Ready. Therefore,
the FQDNs of the ZooKeeper servers will resolve to a single endpoint, and that
endpoint will be the unique ZooKeeper server claiming the identity configured
in its myid file.
When the servers use the Zab protocol to attempt to commit a value, they will either achieve consensus and commit the value (if leader election has succeeded and at least two of the Pods are Running and Ready), or they will fail to do so (if either of the conditions are not met). No state will arise where one server acknowledges a write on behalf of another.
Sanity testing the ensemble
The most basic sanity test is to write data to one ZooKeeper server and
to read the data from another.
The command below executes the zkCli.sh script to write world to the path /hello on the zk-0 Pod in the ensemble.
kubectl exec zk-0 -- zkCli.sh create /hello world
WATCHER::
WatchedEvent state:SyncConnected type:None path:null
Created /hello
To get the data from the zk-1 Pod use the following command.
kubectl exec zk-1 -- zkCli.sh get /hello
The data that you created on zk-0 is available on all the servers in the
ensemble.
WATCHER::
WatchedEvent state:SyncConnected type:None path:null
world
cZxid = 0x100000002
ctime = Thu Dec 08 15:13:30 UTC 2016
mZxid = 0x100000002
mtime = Thu Dec 08 15:13:30 UTC 2016
pZxid = 0x100000002
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 5
numChildren = 0
Providing durable storage
As mentioned in the ZooKeeper Basics section,
ZooKeeper commits all entries to a durable WAL, and periodically writes snapshots
in memory state, to storage media. Using WALs to provide durability is a common
technique for applications that use consensus protocols to achieve a replicated
state machine.
Use the kubectl delete command to delete the
zk StatefulSet.
kubectl delete statefulset zk
statefulset.apps "zk" deleted
Watch the termination of the Pods in the StatefulSet.
kubectl get pods -w -l app=zk
When zk-0 if fully terminated, use CTRL-C to terminate kubectl.
When a Pod in the zkStatefulSet is (re)scheduled, it will always have the
same PersistentVolume mounted to the ZooKeeper server's data directory.
Even when the Pods are rescheduled, all the writes made to the ZooKeeper
servers' WALs, and all their snapshots, remain durable.
Ensuring consistent configuration
As noted in the Facilitating Leader Election and
Achieving Consensus sections, the servers in a
ZooKeeper ensemble require consistent configuration to elect a leader
and form a quorum. They also require consistent configuration of the Zab protocol
in order for the protocol to work correctly over a network. In our example we
achieve consistent configuration by embedding the configuration directly into
the manifest.
The command used to start the ZooKeeper servers passed the configuration as command line parameter. You can also use environment variables to pass configuration to the ensemble.
Configuring logging
One of the files generated by the zkGenConfig.sh script controls ZooKeeper's logging.
ZooKeeper uses Log4j, and, by default,
it uses a time and size based rolling file appender for its logging configuration.
Use the command below to get the logging configuration from one of Pods in the zkStatefulSet.
This is the simplest possible way to safely log inside the container.
Because the applications write logs to standard out, Kubernetes will handle log rotation for you.
Kubernetes also implements a sane retention policy that ensures application logs written to
standard out and standard error do not exhaust local storage media.
Use kubectl logs to retrieve the last 20 log lines from one of the Pods.
kubectl logs zk-0 --tail 20
You can view application logs written to standard out or standard error using kubectl logs and from the Kubernetes Dashboard.
2016-12-06 19:34:16,236 [myid:1] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@827] - Processing ruok command from /127.0.0.1:52740
2016-12-06 19:34:16,237 [myid:1] - INFO [Thread-1136:NIOServerCnxn@1008] - Closed socket connection for client /127.0.0.1:52740 (no session established for client)
2016-12-06 19:34:26,155 [myid:1] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxnFactory@192] - Accepted socket connection from /127.0.0.1:52749
2016-12-06 19:34:26,155 [myid:1] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@827] - Processing ruok command from /127.0.0.1:52749
2016-12-06 19:34:26,156 [myid:1] - INFO [Thread-1137:NIOServerCnxn@1008] - Closed socket connection for client /127.0.0.1:52749 (no session established for client)
2016-12-06 19:34:26,222 [myid:1] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxnFactory@192] - Accepted socket connection from /127.0.0.1:52750
2016-12-06 19:34:26,222 [myid:1] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@827] - Processing ruok command from /127.0.0.1:52750
2016-12-06 19:34:26,226 [myid:1] - INFO [Thread-1138:NIOServerCnxn@1008] - Closed socket connection for client /127.0.0.1:52750 (no session established for client)
2016-12-06 19:34:36,151 [myid:1] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxnFactory@192] - Accepted socket connection from /127.0.0.1:52760
2016-12-06 19:34:36,152 [myid:1] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@827] - Processing ruok command from /127.0.0.1:52760
2016-12-06 19:34:36,152 [myid:1] - INFO [Thread-1139:NIOServerCnxn@1008] - Closed socket connection for client /127.0.0.1:52760 (no session established for client)
2016-12-06 19:34:36,230 [myid:1] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxnFactory@192] - Accepted socket connection from /127.0.0.1:52761
2016-12-06 19:34:36,231 [myid:1] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@827] - Processing ruok command from /127.0.0.1:52761
2016-12-06 19:34:36,231 [myid:1] - INFO [Thread-1140:NIOServerCnxn@1008] - Closed socket connection for client /127.0.0.1:52761 (no session established for client)
2016-12-06 19:34:46,149 [myid:1] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxnFactory@192] - Accepted socket connection from /127.0.0.1:52767
2016-12-06 19:34:46,149 [myid:1] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@827] - Processing ruok command from /127.0.0.1:52767
2016-12-06 19:34:46,149 [myid:1] - INFO [Thread-1141:NIOServerCnxn@1008] - Closed socket connection for client /127.0.0.1:52767 (no session established for client)
2016-12-06 19:34:46,230 [myid:1] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxnFactory@192] - Accepted socket connection from /127.0.0.1:52768
2016-12-06 19:34:46,230 [myid:1] - INFO [NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181:NIOServerCnxn@827] - Processing ruok command from /127.0.0.1:52768
2016-12-06 19:34:46,230 [myid:1] - INFO [Thread-1142:NIOServerCnxn@1008] - Closed socket connection for client /127.0.0.1:52768 (no session established for client)
Kubernetes integrates with many logging solutions. You can choose a logging solution
that best fits your cluster and applications. For cluster-level logging and aggregation,
consider deploying a sidecar container to rotate and ship your logs.
Configuring a non-privileged user
The best practices to allow an application to run as a privileged
user inside of a container are a matter of debate. If your organization requires
that applications run as a non-privileged user you can use a
SecurityContext to control the user that
the entry point runs as.
The zkStatefulSet's Pod template contains a SecurityContext.
securityContext:runAsUser:1000fsGroup:1000
In the Pods' containers, UID 1000 corresponds to the zookeeper user and GID 1000
corresponds to the zookeeper group.
Get the ZooKeeper process information from the zk-0 Pod.
kubectl exec zk-0 -- ps -elf
As the runAsUser field of the securityContext object is set to 1000,
instead of running as root, the ZooKeeper process runs as the zookeeper user.
F S UID PID PPID C PRI NI ADDR SZ WCHAN STIME TTY TIME CMD
4 S zookeep+ 1 0 0 80 0 - 1127 - 20:46 ? 00:00:00 sh -c zkGenConfig.sh && zkServer.sh start-foreground
0 S zookeep+ 27 1 0 80 0 - 1155556 - 20:46 ? 00:00:19 /usr/lib/jvm/java-8-openjdk-amd64/bin/java -Dzookeeper.log.dir=/var/log/zookeeper -Dzookeeper.root.logger=INFO,CONSOLE -cp /usr/bin/../build/classes:/usr/bin/../build/lib/*.jar:/usr/bin/../share/zookeeper/zookeeper-3.4.9.jar:/usr/bin/../share/zookeeper/slf4j-log4j12-1.6.1.jar:/usr/bin/../share/zookeeper/slf4j-api-1.6.1.jar:/usr/bin/../share/zookeeper/netty-3.10.5.Final.jar:/usr/bin/../share/zookeeper/log4j-1.2.16.jar:/usr/bin/../share/zookeeper/jline-0.9.94.jar:/usr/bin/../src/java/lib/*.jar:/usr/bin/../etc/zookeeper: -Xmx2G -Xms2G -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.local.only=false org.apache.zookeeper.server.quorum.QuorumPeerMain /usr/bin/../etc/zookeeper/zoo.cfg
By default, when the Pod's PersistentVolumes is mounted to the ZooKeeper server's data directory, it is only accessible by the root user. This configuration prevents the ZooKeeper process from writing to its WAL and storing its snapshots.
Use the command below to get the file permissions of the ZooKeeper data directory on the zk-0 Pod.
kubectl exec -ti zk-0 -- ls -ld /var/lib/zookeeper/data
Because the fsGroup field of the securityContext object is set to 1000, the ownership of the Pods' PersistentVolumes is set to the zookeeper group, and the ZooKeeper process is able to read and write its data.
drwxr-sr-x 3 zookeeper zookeeper 4096 Dec 5 20:45 /var/lib/zookeeper/data
Managing the ZooKeeper process
The ZooKeeper documentation
mentions that "You will want to have a supervisory process that
manages each of your ZooKeeper server processes (JVM)." Utilizing a watchdog
(supervisory process) to restart failed processes in a distributed system is a
common pattern. When deploying an application in Kubernetes, rather than using
an external utility as a supervisory process, you should use Kubernetes as the
watchdog for your application.
Updating the ensemble
The zkStatefulSet is configured to use the RollingUpdate update strategy.
You can use kubectl patch to update the number of cpus allocated to the servers.
Use kubectl rollout status to watch the status of the update.
kubectl rollout status sts/zk
waiting for statefulset rolling update to complete 0 pods at revision zk-5db4499664...
Waiting for 1 pods to be ready...
Waiting for 1 pods to be ready...
waiting for statefulset rolling update to complete 1 pods at revision zk-5db4499664...
Waiting for 1 pods to be ready...
Waiting for 1 pods to be ready...
waiting for statefulset rolling update to complete 2 pods at revision zk-5db4499664...
Waiting for 1 pods to be ready...
Waiting for 1 pods to be ready...
statefulset rolling update complete 3 pods at revision zk-5db4499664...
This terminates the Pods, one at a time, in reverse ordinal order, and recreates them with the new configuration. This ensures that quorum is maintained during a rolling update.
Use the kubectl rollout history command to view a history or previous configurations.
kubectl rollout history sts/zk
The output is similar to this:
statefulsets "zk"
REVISION
1
2
Use the kubectl rollout undo command to roll back the modification.
kubectl rollout undo sts/zk
The output is similar to this:
statefulset.apps/zk rolled back
Handling process failure
Restart Policies control how
Kubernetes handles process failures for the entry point of the container in a Pod.
For Pods in a StatefulSet, the only appropriate RestartPolicy is Always, and this
is the default value. For stateful applications you should never override
the default policy.
Use the following command to examine the process tree for the ZooKeeper server running in the zk-0 Pod.
kubectl exec zk-0 -- ps -ef
The command used as the container's entry point has PID 1, and
the ZooKeeper process, a child of the entry point, has PID 27.
In another terminal watch the Pods in the zkStatefulSet with the following command.
kubectl get pod -w -l app=zk
In another terminal, terminate the ZooKeeper process in Pod zk-0 with the following command.
kubectl exec zk-0 -- pkill java
The termination of the ZooKeeper process caused its parent process to terminate. Because the RestartPolicy of the container is Always, it restarted the parent process.
NAME READY STATUS RESTARTS AGE
zk-0 1/1 Running 0 21m
zk-1 1/1 Running 0 20m
zk-2 1/1 Running 0 19m
NAME READY STATUS RESTARTS AGE
zk-0 0/1 Error 0 29m
zk-0 0/1 Running 1 29m
zk-0 1/1 Running 1 29m
If your application uses a script (such as zkServer.sh) to launch the process
that implements the application's business logic, the script must terminate with the
child process. This ensures that Kubernetes will restart the application's
container when the process implementing the application's business logic fails.
Testing for liveness
Configuring your application to restart failed processes is not enough to
keep a distributed system healthy. There are scenarios where
a system's processes can be both alive and unresponsive, or otherwise
unhealthy. You should use liveness probes to notify Kubernetes
that your application's processes are unhealthy and it should restart them.
The Pod template for the zkStatefulSet specifies a liveness probe.
When the liveness probe for the ZooKeeper process fails, Kubernetes will
automatically restart the process for you, ensuring that unhealthy processes in
the ensemble are restarted.
kubectl get pod -w -l app=zk
NAME READY STATUS RESTARTS AGE
zk-0 1/1 Running 0 1h
zk-1 1/1 Running 0 1h
zk-2 1/1 Running 0 1h
NAME READY STATUS RESTARTS AGE
zk-0 0/1 Running 0 1h
zk-0 0/1 Running 1 1h
zk-0 1/1 Running 1 1h
Testing for readiness
Readiness is not the same as liveness. If a process is alive, it is scheduled
and healthy. If a process is ready, it is able to process input. Liveness is
a necessary, but not sufficient, condition for readiness. There are cases,
particularly during initialization and termination, when a process can be
alive but not ready.
If you specify a readiness probe, Kubernetes will ensure that your application's
processes will not receive network traffic until their readiness checks pass.
For a ZooKeeper server, liveness implies readiness. Therefore, the readiness
probe from the zookeeper.yaml manifest is identical to the liveness probe.
Even though the liveness and readiness probes are identical, it is important
to specify both. This ensures that only healthy servers in the ZooKeeper
ensemble receive network traffic.
Tolerating Node failure
ZooKeeper needs a quorum of servers to successfully commit mutations
to data. For a three server ensemble, two servers must be healthy for
writes to succeed. In quorum based systems, members are deployed across failure
domains to ensure availability. To avoid an outage, due to the loss of an
individual machine, best practices preclude co-locating multiple instances of the
application on the same machine.
By default, Kubernetes may co-locate Pods in a StatefulSet on the same node.
For the three server ensemble you created, if two servers are on the same node, and that node fails,
the clients of your ZooKeeper service will experience an outage until at least one of the Pods can be rescheduled.
You should always provision additional capacity to allow the processes of critical
systems to be rescheduled in the event of node failures. If you do so, then the
outage will only last until the Kubernetes scheduler reschedules one of the ZooKeeper
servers. However, if you want your service to tolerate node failures with no downtime,
you should set podAntiAffinity.
Use the command below to get the nodes for Pods in the zkStatefulSet.
for i in 01 2; do kubectl get pod zk-$i --template {{.spec.nodeName}}; echo""; done
All of the Pods in the zkStatefulSet are deployed on different nodes.
The requiredDuringSchedulingIgnoredDuringExecution field tells the
Kubernetes Scheduler that it should never co-locate two Pods which have app label
as zk in the domain defined by the topologyKey. The topologyKeykubernetes.io/hostname indicates that the domain is an individual node. Using
different rules, labels, and selectors, you can extend this technique to spread
your ensemble across physical, network, and power failure domains.
Surviving maintenance
In this section you will cordon and drain nodes. If you are using this tutorial
on a shared cluster, be sure that this will not adversely affect other tenants.
The previous section showed you how to spread your Pods across nodes to survive
unplanned node failures, but you also need to plan for temporary node failures
that occur due to planned maintenance.
Use this command to get the nodes in your cluster.
kubectl get nodes
This tutorial assumes a cluster with at least four nodes. If the cluster has more than four, use kubectl cordon to cordon all but four nodes. Constraining to four nodes will ensure Kubernetes encounters affinity and PodDisruptionBudget constraints when scheduling zookeeper Pods in the following maintenance simulation.
kubectl cordon <node-name>
Use this command to get the zk-pdbPodDisruptionBudget.
kubectl get pdb zk-pdb
The max-unavailable field indicates to Kubernetes that at most one Pod from
zkStatefulSet can be unavailable at any time.
NAME MIN-AVAILABLE MAX-UNAVAILABLE ALLOWED-DISRUPTIONS AGE
zk-pdb N/A 1 1
In one terminal, use this command to watch the Pods in the zkStatefulSet.
kubectl get pods -w -l app=zk
In another terminal, use this command to get the nodes that the Pods are currently scheduled on.
for i in 01 2; do kubectl get pod zk-$i --template {{.spec.nodeName}}; echo""; done
Keep watching the StatefulSet's Pods in the first terminal and drain the node on which
zk-1 is scheduled.
kubectl drain $(kubectl get pod zk-1 --template {{.spec.nodeName}}) --ignore-daemonsets --force --delete-emptydir-data
The output is similar to this:
"kubernetes-node-ixsl" cordoned
WARNING: Deleting pods not managed by ReplicationController, ReplicaSet, Job, or DaemonSet: fluentd-cloud-logging-kubernetes-node-ixsl, kube-proxy-kubernetes-node-ixsl; Ignoring DaemonSet-managed pods: node-problem-detector-v0.1-voc74
pod "zk-1" deleted
node "kubernetes-node-ixsl" drained
The zk-1 Pod cannot be scheduled because the zkStatefulSet contains a PodAntiAffinity rule preventing
co-location of the Pods, and as only two nodes are schedulable, the Pod will remain in a Pending state.
Continue to watch the Pods of the StatefulSet, and drain the node on which
zk-2 is scheduled.
kubectl drain $(kubectl get pod zk-2 --template {{.spec.nodeName}}) --ignore-daemonsets --force --delete-emptydir-data
The output is similar to this:
node "kubernetes-node-i4c4" cordoned
WARNING: Deleting pods not managed by ReplicationController, ReplicaSet, Job, or DaemonSet: fluentd-cloud-logging-kubernetes-node-i4c4, kube-proxy-kubernetes-node-i4c4; Ignoring DaemonSet-managed pods: node-problem-detector-v0.1-dyrog
WARNING: Ignoring DaemonSet-managed pods: node-problem-detector-v0.1-dyrog; Deleting pods not managed by ReplicationController, ReplicaSet, Job, or DaemonSet: fluentd-cloud-logging-kubernetes-node-i4c4, kube-proxy-kubernetes-node-i4c4
There are pending pods when an error occurred: Cannot evict pod as it would violate the pod's disruption budget.
pod/zk-2
Use CTRL-C to terminate kubectl.
You cannot drain the third node because evicting zk-2 would violate zk-budget. However, the node will remain cordoned.
Use zkCli.sh to retrieve the value you entered during the sanity test from zk-0.
kubectl exec zk-0 zkCli.sh get /hello
The service is still available because its PodDisruptionBudget is respected.
WatchedEvent state:SyncConnected type:None path:null
world
cZxid = 0x200000002
ctime = Wed Dec 07 00:08:59 UTC 2016
mZxid = 0x200000002
mtime = Wed Dec 07 00:08:59 UTC 2016
pZxid = 0x200000002
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 5
numChildren = 0
Attempt to drain the node on which zk-2 is scheduled.
kubectl drain $(kubectl get pod zk-2 --template {{.spec.nodeName}}) --ignore-daemonsets --force --delete-emptydir-data
The output is similar to this:
node "kubernetes-node-i4c4" already cordoned
WARNING: Deleting pods not managed by ReplicationController, ReplicaSet, Job, or DaemonSet: fluentd-cloud-logging-kubernetes-node-i4c4, kube-proxy-kubernetes-node-i4c4; Ignoring DaemonSet-managed pods: node-problem-detector-v0.1-dyrog
pod "heapster-v1.2.0-2604621511-wht1r" deleted
pod "zk-2" deleted
node "kubernetes-node-i4c4" drained
This time kubectl drain succeeds.
Uncordon the second node to allow zk-2 to be rescheduled.
kubectl uncordon kubernetes-node-ixsl
The output is similar to this:
node "kubernetes-node-ixsl" uncordoned
You can use kubectl drain in conjunction with PodDisruptionBudgets to ensure that your services remain available during maintenance.
If drain is used to cordon nodes and evict pods prior to taking the node offline for maintenance,
services that express a disruption budget will have that budget respected.
You should always allocate additional capacity for critical services so that their Pods can be immediately rescheduled.
Cleaning up
Use kubectl uncordon to uncordon all the nodes in your cluster.
You must delete the persistent storage media for the PersistentVolumes used in this tutorial.
Follow the necessary steps, based on your environment, storage configuration,
and provisioning method, to ensure that all storage is reclaimed.
7 - Services
7.1 - Connecting Applications with Services
The Kubernetes model for connecting containers
Now that you have a continuously running, replicated application you can expose it on a network.
Kubernetes assumes that pods can communicate with other pods, regardless of which host they land on. Kubernetes gives every pod its own cluster-private IP address, so you do not need to explicitly create links between pods or map container ports to host ports. This means that containers within a Pod can all reach each other's ports on localhost, and all pods in a cluster can see each other without NAT. The rest of this document elaborates on how you can run reliable services on such a networking model.
This tutorial uses a simple nginx web server to demonstrate the concept.
Exposing pods to the cluster
We did this in a previous example, but let's do it once again and focus on the networking perspective.
Create an nginx Pod, and note that it has a container port specification:
NAME READY STATUS RESTARTS AGE IP NODE
my-nginx-3800858182-jr4a2 1/1 Running 0 13s 10.244.3.4 kubernetes-minion-905m
my-nginx-3800858182-kna2y 1/1 Running 0 13s 10.244.2.5 kubernetes-minion-ljyd
Check your pods' IPs:
kubectl get pods -l run=my-nginx -o custom-columns=POD_IP:.status.podIPs
POD_IP
[map[ip:10.244.3.4]][map[ip:10.244.2.5]]
You should be able to ssh into any node in your cluster and use a tool such as curl to make queries against both IPs. Note that the containers are not using port 80 on the node, nor are there any special NAT rules to route traffic to the pod. This means you can run multiple nginx pods on the same node all using the same containerPort, and access them from any other pod or node in your cluster using the assigned IP address for the Service. If you want to arrange for a specific port on the host Node to be forwarded to backing Pods, you can - but the networking model should mean that you do not need to do so.
So we have pods running nginx in a flat, cluster wide, address space. In theory, you could talk to these pods directly, but what happens when a node dies? The pods die with it, and the Deployment will create new ones, with different IPs. This is the problem a Service solves.
A Kubernetes Service is an abstraction which defines a logical set of Pods running somewhere in your cluster, that all provide the same functionality. When created, each Service is assigned a unique IP address (also called clusterIP). This address is tied to the lifespan of the Service, and will not change while the Service is alive. Pods can be configured to talk to the Service, and know that communication to the Service will be automatically load-balanced out to some pod that is a member of the Service.
You can create a Service for your 2 nginx replicas with kubectl expose:
kubectl expose deployment/my-nginx
service/my-nginx exposed
This is equivalent to kubectl apply -f the following yaml:
This specification will create a Service which targets TCP port 80 on any Pod
with the run: my-nginx label, and expose it on an abstracted Service port
(targetPort: is the port the container accepts traffic on, port: is the
abstracted Service port, which can be any port other pods use to access the
Service).
View Service
API object to see the list of supported fields in service definition.
Check your Service:
kubectl get svc my-nginx
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
my-nginx ClusterIP 10.0.162.149 <none> 80/TCP 21s
As mentioned previously, a Service is backed by a group of Pods. These Pods are
exposed through
EndpointSlices.
The Service's selector will be evaluated continuously and the results will be POSTed
to an EndpointSlice that is connected to the Service using a
labels.
When a Pod dies, it is automatically removed from the EndpointSlices that contain it
as an endpoint. New Pods that match the Service's selector will automatically get added
to an EndpointSlice for that Service.
Check the endpoints, and note that the IPs are the same as the Pods created in
the first step:
kubectl get endpointslices -l kubernetes.io/service-name=my-nginx
NAME ADDRESSTYPE PORTS ENDPOINTS AGE
my-nginx-7vzhx IPv4 80 10.244.2.5,10.244.3.4 21s
You should now be able to curl the nginx Service on <CLUSTER-IP>:<PORT> from
any node in your cluster. Note that the Service IP is completely virtual, it
never hits the wire. If you're curious about how this works you can read more
about the service proxy.
Accessing the Service
Kubernetes supports 2 primary modes of finding a Service - environment variables
and DNS. The former works out of the box while the latter requires the
CoreDNS cluster addon.
Note: If the service environment variables are not desired (because possible clashing with expected program ones,
too many variables to process, only using DNS, etc) you can disable this mode by setting the enableServiceLinks
flag to false on the pod spec.
Environment Variables
When a Pod runs on a Node, the kubelet adds a set of environment variables for
each active Service. This introduces an ordering problem. To see why, inspect
the environment of your running nginx Pods (your Pod name will be different):
kubectl exec my-nginx-3800858182-jr4a2 -- printenv | grep SERVICE
Note there's no mention of your Service. This is because you created the replicas
before the Service. Another disadvantage of doing this is that the scheduler might
put both Pods on the same machine, which will take your entire Service down if
it dies. We can do this the right way by killing the 2 Pods and waiting for the
Deployment to recreate them. This time around the Service exists before the
replicas. This will give you scheduler-level Service spreading of your Pods
(provided all your nodes have equal capacity), as well as the right environment
variables:
Kubernetes offers a DNS cluster addon Service that automatically assigns dns names to other Services. You can check if it's running on your cluster:
kubectl get services kube-dns --namespace=kube-system
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kube-dns ClusterIP 10.0.0.10 <none> 53/UDP,53/TCP 8m
The rest of this section will assume you have a Service with a long lived IP
(my-nginx), and a DNS server that has assigned a name to that IP. Here we use the CoreDNS cluster addon (application name kube-dns), so you can talk to the Service from any pod in your cluster using standard methods (e.g. gethostbyname()). If CoreDNS isn't running, you can enable it referring to the CoreDNS README or Installing CoreDNS. Let's run another curl application to test this:
kubectl run curl --image=radial/busyboxplus:curl -i --tty
Waiting for pod default/curl-131556218-9fnch to be running, status is Pending, pod ready: false
Hit enter for command prompt
Till now we have only accessed the nginx server from within the cluster. Before exposing the Service to the internet, you want to make sure the communication channel is secure. For this, you will need:
Self signed certificates for https (unless you already have an identity certificate)
An nginx server configured to use the certificates
A secret that makes the certificates accessible to pods
You can acquire all these from the nginx https example. This requires having go and make tools installed. If you don't want to install those, then follow the manual steps later. In short:
At this point you can reach the nginx server from any node.
kubectl get pods -l run=my-nginx -o custom-columns=POD_IP:.status.podIPs
POD_IP
[map[ip:10.244.3.5]]
node $ curl -k https://10.244.3.5
...
<h1>Welcome to nginx!</h1>
Note how we supplied the -k parameter to curl in the last step, this is because we don't know anything about the pods running nginx at certificate generation time,
so we have to tell curl to ignore the CName mismatch. By creating a Service we linked the CName used in the certificate with the actual DNS name used by pods during Service lookup.
Let's test this from a pod (the same secret is being reused for simplicity, the pod only needs nginx.crt to access the Service):
For some parts of your applications you may want to expose a Service onto an
external IP address. Kubernetes supports two ways of doing this: NodePorts and
LoadBalancers. The Service created in the last section already used NodePort,
so your nginx HTTPS replica is ready to serve traffic on the internet if your
node has a public IP.
Let's now recreate the Service to use a cloud load balancer. Change the Type of my-nginx Service from NodePort to LoadBalancer:
kubectl edit svc my-nginx
kubectl get svc my-nginx
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
my-nginx LoadBalancer 10.0.162.149 xx.xxx.xxx.xxx 8080:30163/TCP 21s
curl https://<EXTERNAL-IP> -k
...
<title>Welcome to nginx!</title>
The IP address in the EXTERNAL-IP column is the one that is available on the public internet. The CLUSTER-IP is only available inside your
cluster/private cloud network.
Note that on AWS, type LoadBalancer creates an ELB, which uses a (long)
hostname, not an IP. It's too long to fit in the standard kubectl get svc
output, in fact, so you'll need to do kubectl describe service my-nginx to
see it. You'll see something like this:
kubectl describe service my-nginx
...
LoadBalancer Ingress: a320587ffd19711e5a37606cf4a74574-1142138393.us-east-1.elb.amazonaws.com
...
Applications running in a Kubernetes cluster find and communicate with each
other, and the outside world, through the Service abstraction. This document
explains what happens to the source IP of packets sent to different types
of Services, and how you can toggle this behavior according to your needs.
a network daemon that orchestrates Service VIP management on every node
Prerequisites
You need to have a Kubernetes cluster, and the kubectl command-line tool must
be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a
cluster, you can create one by using
minikube
or you can use one of these Kubernetes playgrounds:
Expose a simple application through various types of Services
Understand how each Service type handles source IP NAT
Understand the tradeoffs involved in preserving source IP
Source IP for Services with Type=ClusterIP
Packets sent to ClusterIP from within the cluster are never source NAT'd if
you're running kube-proxy in
iptables mode,
(the default). You can query the kube-proxy mode by fetching
http://localhost:10249/proxyMode on the node where kube-proxy is running.
kubectl get nodes
The output is similar to this:
NAME STATUS ROLES AGE VERSION
kubernetes-node-6jst Ready <none> 2h v1.13.0
kubernetes-node-cx31 Ready <none> 2h v1.13.0
kubernetes-node-jj1t Ready <none> 2h v1.13.0
Get the proxy mode on one of the nodes (kube-proxy listens on port 10249):
# Run this in a shell on the node you want to query.curl http://localhost:10249/proxyMode
The output is:
iptables
You can test source IP preservation by creating a Service over the source IP app:
NODEPORT=$(kubectl get -o jsonpath="{.spec.ports[0].nodePort}" services nodeport)NODES=$(kubectl get nodes -o jsonpath='{ $.items[*].status.addresses[?(@.type=="InternalIP")].address }')
If you're running on a cloud provider, you may need to open up a firewall-rule
for the nodes:nodeport reported above.
Now you can try reaching the Service from outside the cluster through the node
port allocated above.
for node in $NODES; do curl -s $node:$NODEPORT | grep -i client_address; done
Note that these are not the correct client IPs, they're cluster internal IPs. This is what happens:
Client sends packet to node2:nodePort
node2 replaces the source IP address (SNAT) in the packet with its own IP address
node2 replaces the destination IP on the packet with the pod IP
packet is routed to node 1, and then to the endpoint
the pod's reply is routed back to node2
the pod's reply is sent back to the client
Visually:
Figure. Source IP Type=NodePort using SNAT
To avoid this, Kubernetes has a feature to
preserve the client source IP.
If you set service.spec.externalTrafficPolicy to the value Local,
kube-proxy only proxies proxy requests to local endpoints, and does not
forward traffic to other nodes. This approach preserves the original
source IP address. If there are no local endpoints, packets sent to the
node are dropped, so you can rely on the correct source-ip in any packet
processing rules you might apply a packet that make it through to the
endpoint.
Set the service.spec.externalTrafficPolicy field as follows:
for node in $NODES; do curl --connect-timeout 1 -s $node:$NODEPORT | grep -i client_address; done
The output is similar to:
client_address=198.51.100.79
Note that you only got one reply, with the right client IP, from the one node on which the endpoint pod
is running.
This is what happens:
client sends packet to node2:nodePort, which doesn't have any endpoints
packet is dropped
client sends packet to node1:nodePort, which does have endpoints
node1 routes packet to endpoint with the correct source IP
Visually:
Figure. Source IP Type=NodePort preserves client source IP address
Source IP for Services with Type=LoadBalancer
Packets sent to Services with
Type=LoadBalancer
are source NAT'd by default, because all schedulable Kubernetes nodes in the
Ready state are eligible for load-balanced traffic. So if packets arrive
at a node without an endpoint, the system proxies it to a node with an
endpoint, replacing the source IP on the packet with the IP of the node (as
described in the previous section).
You can test this by exposing the source-ip-app through a load balancer:
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
loadbalancer LoadBalancer 10.0.65.118 203.0.113.140 80/TCP 5m
Next, send a request to this Service's external-ip:
curl 203.0.113.140
The output is similar to this:
CLIENT VALUES:
client_address=10.240.0.5
...
However, if you're running on Google Kubernetes Engine/GCE, setting the same service.spec.externalTrafficPolicy
field to Local forces nodes without Service endpoints to remove
themselves from the list of nodes eligible for loadbalanced traffic by
deliberately failing health checks.
You should immediately see the service.spec.healthCheckNodePort field allocated
by Kubernetes:
kubectl get svc loadbalancer -o yaml | grep -i healthCheckNodePort
The output is similar to this:
healthCheckNodePort:32122
The service.spec.healthCheckNodePort field points to a port on every node
serving the health check at /healthz. You can test this:
kubectl get pod -o wide -l app=source-ip-app
The output is similar to this:
NAME READY STATUS RESTARTS AGE IP NODE
source-ip-app-826191075-qehz4 1/1 Running 0 20h 10.180.1.136 kubernetes-node-6jst
Use curl to fetch the /healthz endpoint on various nodes:
# Run this locally on a node you choosecurl localhost:32122/healthz
1 Service Endpoints found
On a different node you might get a different result:
# Run this locally on a node you choosecurl localhost:32122/healthz
No Service Endpoints Found
A controller running on the
control plane is
responsible for allocating the cloud load balancer. The same controller also
allocates HTTP health checks pointing to this port/path on each node. Wait
about 10 seconds for the 2 nodes without endpoints to fail health checks,
then use curl to query the IPv4 address of the load balancer:
curl 203.0.113.140
The output is similar to this:
CLIENT VALUES:
client_address=198.51.100.79
...
Cross-platform support
Only some cloud providers offer support for source IP preservation through
Services with Type=LoadBalancer.
The cloud provider you're running on might fulfill the request for a loadbalancer
in a few different ways:
With a proxy that terminates the client connection and opens a new connection
to your nodes/endpoints. In such cases the source IP will always be that of the
cloud LB, not that of the client.
With a packet forwarder, such that requests from the client sent to the
loadbalancer VIP end up at the node with the source IP of the client, not
an intermediate proxy.
Load balancers in the first category must use an agreed upon
protocol between the loadbalancer and backend to communicate the true client IP
such as the HTTP Forwarded
or X-FORWARDED-FOR
headers, or the
proxy protocol.
Load balancers in the second category can leverage the feature described above
by creating an HTTP health check pointing at the port stored in
the service.spec.healthCheckNodePort field on the Service.
