I am again and again downloading and install a package whenever a pod restarts so how can I automate it. I wanted the pod to automatically install or download a package when the pod restarts.how can I do it in Kubernetes?
Option 1 (best practice):
If you want the package to be downloaded and installed in the container inside of the Pod when it starts, then you must add those download and install instructions to the Dockerfile using the RUN directive.
If you’re using a public image, and not your own custom image, then you’ll want to create a Dockerfile and use the public image as the base image to create and push your own custom Docker image to a image repository. You do this by adding the FROM directive as the first line of the Dockerfile.
There are a ton of tutorials out there on how to build images with Dockerfiles and push them to a repository for use by Kubernetes. Here’s the official documentation from Docker which explains the aforementioned directives and everything else you need to know to create Dockerfiles, build them into Docker images, and push them to a image repository like Docker Hub.
In short, you’ll end up with a Dockerfile that looks something like this, which adds the instructions to download and install the package to a base image:
FROM <base image (i.e. the image you’re currently using)>
RUN <download command>
RUN <install command>The linked documentation tells you how to build and push a Docker image to a repo, and then it’s just a matter of updating the image field in your Pod manifest.
Now whenever your Pod restarts it will already have the package installed.
Option 2 (anti-pattern, not recommended):
Caution: I'm including this option because OP does not want to use Option 1, so I'm including one possible, theoretical alternative.
You could use an init container to accomplish this. The init container would need to download and install a package for your app container and put it in a mounted emptyDir volume shared by the init container and app container. This work would be done using the command property in the init container.
After your init container runs, your app container can access the package via the mounted shared emptyDir volume.
More about sharing data between containers.
There are several reasons I could think of off the top of my head for why this is an anti-pattern:
It slows down Pod startup time.
Your emptyDir volume is mutable and if you somehow delete or corrupt the package, and your app container (not Pod) crashes, your Pod will crash loop as your init container only runs on Pod restarts, not container restarts.
It unnecessarily complicates your Pod manifest.
A pod should be complete - it shouldn't need to download and install a package. You are essentially trying to do a 'build step' during pod startup, this is almost certainly an anti-pattern.
If the image you are using doesn't contain a package then you should build your own image and deploy it to a docker registry or look for a different docker image that contains your required package.
ericstaples has done a good job of explaining how to roll your own docker image and push it do a docker repository.
If you edit your question and provide the image repo:tag that you are currently using and also the package you want to install then you may receive better responses.