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Luke Vincent
Luke Vincent

Reputation: 1323

Kubernetes allow container to exit without pod restart

A fairly common setup I see for docker is to have a container spin up perform a task and then exit. This is something I do quite often with docker-compose where I have a node container that performs a build process and doesn't need to stay up once the static files have been built. In these cases if I look at the docker-compose ps output, while my other containers are up and exposed on a port, the node containers state will be "Exit 0". Although otherwise dormant if I need to access this container it's available to be spun up.

What's a good practice for translating this setup to Kubernetes?

My initial approach was to place everything in one pod but the container exiting causes a CrashLoopBackOff and due to the pod restart policy the pod keeps restarting. If I were to keep this setup I'd only want the pod to restart if one of the other containers were to fail. It already moves the build static files into a volume that is accessible by the other containers.

Should this container be moved into another pod that does not restart? Seems like this would unnecessarily complicate the deployment.

Upvotes: 3

Views: 6817

Answers (2)

David Maze
David Maze

Reputation: 158647

a node container that performs a build process and doesn't need to stay up once the static files have been built

That sounds like exactly the definition of an init container: "They always run to completion. Each one must run successfully before the next one is started."

In your Deployment spec, in the Pod template part, you'd have a separate initContainers: section that contains the separate build-only container. It has the exact same format as the containers: section that contains the main application, but runs first, to completion, once. You may need to create a volume within the context of the Pod to share contents with the main container, but this can be something like an emptyDir: type pod with no actual persistent storage.

If you really are "building" something in the sense of running a tool like Webpack that mostly generates static files, it's better still to move this process into a Dockerfile, so that you can run the unmodified image without doing still more building at deploy time.

Upvotes: 4

WindyFields
WindyFields

Reputation: 2875

Generally, to prevent POD from restating use restartPolicy: Never (more on Restart Policy).

Also, for the thing which you want to run "to completion" use k8s component called Job (more on Job):

apiVersion: batch/v1
kind: Job
metadata:
  name: <job_name>
spec:
  template:
    spec:
      containers:
      <...>

To run Job till the first success (which is exit code 0) set restartPolicy: OnFailure.

Upvotes: 9

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