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:

apiVersion: v1
kind: Pod
  name: init-demo
  - name: nginx
    image: nginx
    - containerPort: 80
    - name: workdir
      mountPath: /usr/share/nginx/html
  # These containers are run during pod initialization
  - name: install
    image: busybox:1.28
    - wget
    - "-O"
    - "/work-dir/index.html"
    - name: workdir
      mountPath: "/work-dir"
  dnsPolicy: Default
  - name: workdir
    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:

wget -O /work-dir/index.html

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

Create the Pod:

kubectl apply -f

Verify that the nginx container is running:

kubectl get pod init-demo

The output shows that the nginx container is running:

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:


<h1> - home of the first website</h1>
  <li><a href="">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)