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Why kubernetes pod fails to run docker image – Debian

I create a simple executable binary file program that runs forever:

// pseudocode
while (true) {
    print("Sleeping")
    sleep(seconds(1));
}

Then I dockerise this program using such Dockerfile:

FROM debian:10
ADD program /
ENTRYPOINT ["/program"]

Then I build and push docker image to a global repository:

docker build -t docker:5000/program .
docker push docker:5000/program

Then I create a deploy.yaml file for this program to be run on a kubernetes pod:

apiVersion: v1
kind: Pod
metadata:
 name: program
 namespace: my_namespace
spec:
 containers:
  - name: program
    image: docker:5000/program
    imagePullPolicy: Always
    command: ["echo", "SUCCESS"]

Finally, I start the program on kubernetes:

kubectl create -f deploy.yaml

However, the kubectl describe pods -n my_namespace program reports:

Events:
  Type     Reason     Age                 From                         Message
  ----     ------     ----                ----                         -------
  Normal   Scheduled  27m                 default-scheduler            Successfully assigned 
mariusl/ingress to mma7-standard5-ime
  Normal   Created    26m (x4 over 27m)   kubelet, mma7-standard5-ime  Created container 
ingress
  Normal   Started    26m (x4 over 27m)   kubelet, mma7-standard5-ime  Started container 
ingress
  Normal   Pulling    25m (x5 over 27m)   kubelet, mma7-standard5-ime  Pulling image 
"docker:5000/program"
  Normal   Pulled     25m (x5 over 27m)   kubelet, mma7-standard5-ime  Successfully pulled 
image "docker:5000/program"
  Warning  BackOff    2m (x117 over 27m)  kubelet, mma7-standard5-ime  Back-off restarting 
failed container

Which, in my interpretation means, that the program fails to get executed and gets repeatedly restarted. Why can this happen?

Tags:

3

Answers


  1. 0

    Your container executes echo “SUCCESS” and terminates, see
    https://kubernetes.io/docs/tasks/inject-data-application/define-command-argument-container/#notes

    command in kubernetes overrides entrypoint in docker. But this does not explain why the container is failed.

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  2. 0

    Your pod is configured with command: ["echo", "SUCCESS"] which will overwrite the ENTRYPOINT ["/program"] and hence, your container will only echo SUCCESS and terminate immediately.

    Note that in Kubernetes, command will overwrite entrypoint in Docker container and args will overwrite cmd in Docker container.

    You can remove the line command: ["echo", "SUCCESS"] and the pod will be up and running!

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  3. 0

    When you override the default Entrypoint and Cmd, these rules apply: read here

    1) If you do not supply command or args for a Container, the defaults defined in the Docker image are used.

    2) If you supply a command but no args for a Container, only the supplied command is used. The default EntryPoint and the default Cmd defined in the Docker image are ignored.

    3) If you supply only args for a Container, the default Entrypoint defined in the Docker image is run with the args that you supplied.

    4) If you supply a command and args, the default Entrypoint and the default Cmd defined in the Docker image are ignored. Your command is run with your args.

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