Configure Pod Initialization

This page shows how to use an Init Container to initialize a Pod before an application Container runs.

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:

To check the version, enter kubectl version.

Create a Pod that has an Init Container

In this exercise you create a Pod that has one application Container and one Init Container. The init container runs to completion before the application container starts.

Here is the configuration file for the Pod:

pods/init-containers.yaml Configure Pod Initialization - 图1

  1. apiVersion: v1
  2. kind: Pod
  3. metadata:
  4.   name: init-demo
  5. spec:
  6.   containers:
  7.   - name: nginx
  8.     image: nginx
  9.     ports:
  10.     - containerPort: 80
  11.     volumeMounts:
  12.     - name: workdir
  13.       mountPath: /usr/share/nginx/html
  14.   # These containers are run during pod initialization
  15.   initContainers:
  16.   - name: install
  17.     image: busybox:1.28
  18.     command:
  19.     - wget
  20.     - "-O"
  21.     - "/work-dir/index.html"
  22.     - http://info.cern.ch
  23.     volumeMounts:
  24.     - name: workdir
  25.       mountPath: "/work-dir"
  26.   dnsPolicy: Default
  27.   volumes:
  28.   - name: workdir
  29.     emptyDir: {}

In the configuration file, you can see that the Pod has a Volume that the init container and the application container share.

The init container mounts the shared Volume at /work-dir, and the application container mounts the shared Volume at /usr/share/nginx/html. The init container runs the following command and then terminates:

  1. wget -O /work-dir/index.html http://info.cern.ch

Notice that the init container writes the index.html file in the root directory of the nginx server.

Create the Pod:

  1. kubectl apply -f https://k8s.io/examples/pods/init-containers.yaml

Verify that the nginx container is running:

  1. kubectl get pod init-demo

The output shows that the nginx container is running:

  1. NAME        READY     STATUS    RESTARTS   AGE
  2. init-demo   1/1       Running   0          1m

Get a shell into the nginx container running in the init-demo Pod:

  1. kubectl exec -it init-demo -- /bin/bash

In your shell, send a GET request to the nginx server:

  1. root@nginx:~# apt-get update
  2. root@nginx:~# apt-get install curl
  3. root@nginx:~# curl localhost

The output shows that nginx is serving the web page that was written by the init container:

  1. <html><head></head><body><header>
  2. <title>http://info.cern.ch</title>
  3. </header>
  5. <h1>http://info.cern.ch - home of the first website</h1>
  6.   ...
  7.   <li><a href="http://info.cern.ch/hypertext/WWW/TheProject.html">Browse the first website</a></li>
  8.   ...

What’s next