How can I keep a container running on Kubernetes?

Question

Containers are meant to run to completion. You need to provide your container with a task that will never finish. Something like this should work:

apiVersion: v1
kind: Pod
metadata:
  name: ubuntu
spec:
  containers:
  - name: ubuntu
    image: ubuntu:latest
    # Just spin & wait forever
    command: [ "/bin/bash", "-c", "--" ]
    args: [ "while true; do sleep 30; done;" ]

You could use this CMD in your Dockerfile:

CMD exec /bin/bash -c "trap : TERM INT; sleep infinity & wait"

This will keep your container alive until it is told to stop. Using trap and wait will make your container react immediately to a stop request. Without trap/wait stopping will take a few seconds.

For busybox based images (used in alpine based images) sleep does not know about the infinity argument. This workaround gives you the same immediate response to a docker stop like in the above example:

CMD exec /bin/sh -c "trap : TERM INT; sleep 9999999999d & wait"

A container exits when its main process exits. Doing something like:

docker run -itd debian

to hold the container open is frankly a hack that should only be used for quick tests and examples. If you just want a container for testing for a few minutes, I would do:

docker run -d debian sleep 300

Which has the advantage that the container will automatically exit if you forget about it. Alternatively, you could put something like this in a while loop to keep it running forever, or just run an application such as top. All of these should be easy to do in Kubernetes.

The real question is why would you want to do this? Your container should be providing a service, whose process will keep the container running in the background.

1. In your Dockerfile use this command:

   CMD ["sh", "-c", "tail -f /dev/null"]
   

2. Build your docker image.

3. Push it to your cluster or similar, just to make sure the image it's available.

4. kubectl run debug-container -it --image=<your-image>