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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
apiVersion:v1kind:Podmetadata:name:init-demospec:containers:- name:nginximage:nginxports:- containerPort:80volumeMounts:- name:workdirmountPath:/usr/share/nginx/html# These containers are run during pod initializationinitContainers:- name:installimage:busybox:1.28command:- wget- "-O"- "/work-dir/index.html"- http://info.cern.chvolumeMounts:- name:workdirmountPath:"/work-dir"dnsPolicy:Defaultvolumes:- name:workdiremptyDir:{}

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:

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:

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

Verify that the nginx container is running:

kubectl get pod init-demo

The output shows that the nginx container is running:

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

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

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

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

root@nginx:~# apt-get update root@nginx:~# apt-get install curl root@nginx:~# curl localhost

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

<html><head></head><body><header> <title>http://info.cern.ch</title> </header> <h1>http://info.cern.ch - home of the first website</h1>  ...  <li><ahref="http://info.cern.ch/hypertext/WWW/TheProject.html">Browse the first website</a></li>  ...

What's next

Last modified August 24, 2023 at 6:38 PM PST: Use code_sample shortcode instead of code shortcode (e8b136c3b3)