How can I keep a container running on Kubernetes

Question

I m now trying to run a simple container with shell   bin bash  on a Kubernetes cluster   I thought that there was a way to keep a container running on a 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 an option like this in Kubernetes   I ve tried running a container by using a kubectl run-container command like   kubectl run-container test container ubuntu latest --replicas 1   But the container exits for a few seconds  just like launching with the docker run command without options I mentioned above   And ReplicationController launches it again repeatedly   Is there a way to keep a container running on Kubernetes like the -td options in the docker run command

User · Answer

In order to keep a POD running it should to be performing certain task, otherwise Kubernetes will find it unnecessary, therefore it stops. There are many ways to keep a POD running.

I have faced similar problems when I needed a POD just to run continuously without doing any useful operation. The following are the two ways those worked for me:

Firing up a sleep command while running the container.
Running an infinite loop inside the container.

Although the first option is easier than the second one and may suffice the requirement, it is not the best option. As, there is a limit as far as the number of seconds you are going to assign in the sleep command. But a container with infinite loop running inside it never exits.

However, I will describe both the ways(Considering you are running busybox container):

1. Sleep Command

apiVersion: v1
kind: Pod
metadata:
  name: busybox
  labels:
    app: busybox
spec:
  containers:
  - name: busybox
    image: busybox
    ports:
    - containerPort: 80
    command: ["/bin/sh", "-ec", "sleep 1000"]
  nodeSelector:
    beta.kubernetes.io/os: linux

2. Infinite Loop

apiVersion: v1
kind: Pod
metadata:
  name: busybox
  labels:
    app: busybox
spec:
  containers:
  - name: busybox
    image: busybox
    ports:
    - containerPort: 80
    command: ["/bin/sh", "-ec", "while :; do echo '.'; sleep 5 ; done"]
  nodeSelector:
    beta.kubernetes.io/os: linux

Run the following command to run the pod:

kubectl apply -f <pod-yaml-file-name>.yaml

Hope it helps!

User · Answer

There are many different ways for accomplishing this  but one of the most elegant one is   kubectl run -i --tty --image ubuntu latest ubuntu-test --restart Never --rm  bin sh

User · Answer

My few cents on the subject  Assuming that kubectl is working then the closest command that would be equivalent to the docker command that you mentioned in your question  would be something like this     kubectl run ubuntu --image ubuntu --restart Never --command sleep infinity   Above command will create a single Pod in default namespace and  it will execute sleep command with infinity argument -this way you will have a process that runs in foreground keeping container alive    Afterwords  you can interact with Pod by running kubectl exec command      kubectl exec ubuntu -it -- bash   This technique is very useful for creating a Pod resource and ad-hoc debugging

User · Answer

You could use this CMD in your Dockerfile  CMD exec  bin bash -c  quot trap   TERM INT  sleep infinity  amp  wait quot   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  quot trap   TERM INT  sleep 9999999999d  amp  wait quot

User · Answer

I did a hack by putting it in background   root localhost     kubectl run hello -it --image ubuntu -- bash  amp   2  128461  Exec on pod hello  root localhost     kubectl exec -it hello -- whoami root  root localhost     kubectl exec -it hello -- hostname hello  Getting a shell  root localhost     kubectl exec -it hello -- bash root hello    ls bin  boot  dev  etc  home  lib  lib32  lib64  libx32  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

User · Answer

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  -

User · Answer

The simplest command as it can be for k8s pod manifest to run container forever   apiVersion  v1 kind  Pod metadata    name  ubuntu spec    containers    - name  ubuntu     image  ubuntu latest       Just sleep forever     command     sleep        args     infinity

User · Answer

Use Kubernetes Deployment and services

User · Answer

In your Dockerfile use this command   CMD   sh    -c    tail -f  dev null    Build your docker image  Push it to your cluster or similar  just to make sure the image it s available  kubectl run debug-container -it --image  lt your-image gt

User · Answer

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

User · Answer

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  amp  wait forever     command      bin bash    -c    --        args     while true  do sleep 30  done

User · Answer

Use this command inside you Dockerfile to keep the container running in your K8s cluster    CMD tail -f  dev null

User · Answer

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

[docker] How can I keep a container running on Kubernetes?

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