How can I keep container running on Kubernetes?

问题:

I'm now trying to run a simple container with shell(/bin/bash) on Kubernetes Cluster.

I thought that there is a way to keep container running on docker container by using pseudo-tty and detach option(-td option on docker run command).

For Example

$ sudo docker run -td ubuntu:latest

Is there any option like this in kubernetes?

I've tried running container by using kubectl run-container command like

kubectl run-container test_container ubuntu:latest --replicas=1

but container exits in few seconds (just like launching with docker run command without options I mentioned above.) and ReplicationController launches it again repeatedly.

Is there any way to keep container runnning on Kubernetes like -td options in docker run command?

回答1:

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.

回答2:

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; (while true; do sleep 1000; done) & wait"

回答3:

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;" ]

回答4:

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>

回答5:

I was able to get this to work with the command sleep infinity in kubernetes, which will keep the container open. See this answer for alternatives when that doesn't work.

回答6:

In my case, a pod with an initContainer failed to initialize. Running docker ps -a and then docker logs exited-container-id-here gave me a log message which kubectl logs podname didn't display. Mystery solved :-)