configure kubectl to reach cluster on docker

Question

I'm facing an interesting challenge, I'm trying to run kubectl in a docker image with a proper configuration, to reach my cluster.

I've been able to create the image, kubecod

    FROM ubuntu:xenial
    
    WORKDIR /project
    
    RUN apt-get update && apt-get install -y \
        curl
    
    RUN curl -LO https://storage.googleapis.com/kubernetes-release/release/v1.21.0/bin/linux/amd64/kubectl
    
    RUN chmod +x ./kubectl
    
    RUN mv ./kubectl /usr/local/bin/kubectl
    
    ENTRYPOINT ["kubectl"]
    #
    CMD ["version"]

When I run the image, the container is functionning correctly, giving me the expected answer.

Client Version: version.Info{Major:"1", Minor:"19", GitVersion:"v1.19.2", GitCommit:"f5743093fd1c663cb0cbc89748f730662345d44d", GitTreeState:"clean", BuildDate:"2020-09-16T13:41:02Z", GoVersion:"go1.15", Compiler:"gc", Platform:"linux/amd64"} Server Version: version.Info{Major:"1", Minor:"18+", GitVersion:"v1.18.9-eks-d1db3c", GitCommit:"d1db3c46e55f95d6a7d3e5578689371318f95ff9", GitTreeState:"clean", BuildDate:"2020-10-20T22:18:07Z", GoVersion:"go1.13.15", Compiler:"gc", Platform:"linux/amd64"}

However, my aim is to create an image with the kubectl connecting to my node. Reading the doc , I need to add a configuration file in the following folder ~/.kube/config

I've created another Dockerfile to build another image, kubedock , with the proper config file and the creation of the requisite directory, .kube

FROM ubuntu:xenial

#setup a working directory
WORKDIR /project 

RUN apt-get update && apt-get install -y \
    curl

RUN curl -LO https://storage.googleapis.com/kubernetes-release/release/v1.21.0/bin/linux/amd64/kubectl

RUN chmod +x ./kubectl

RUN mv ./kubectl /usr/local/bin/kubectl

#create the directory 
RUN mkdir .kube

#Copy the config file to the .kube folder
COPY ./config .kube

ENTRYPOINT ["kubectl"]

CMD ["cluster-info dump"]

However, when I run the new image in a container, I have the following message

me@os:~/_projects/kubedock$ docker run --name kubecont kubedock
Error: unknown command "cluster-info dump" for "kubectl"
Run 'kubectl --help' for usage.

Not sure what I'm missing.

Any hints are welcomed.

Cheers.

Answer 1

It's not clear to me where your K8s cluster is running, If you run your cluster in GKE you will need to run something like:

gcloud container clusters get-credentials $CLUSTER_NAME --zone $CLUSTER_ZONE

Which will create the ~/.config/gcloud tree of files in the users home directory.

On AWS EKS you will need to setup ~/.aws/credentials and other IAM settings.

I suggest you post the details of where your K8s cluster is running and we can take it from there.

PS maybe if you mount/copy the host home directory of a working user into the docker it will work.

Answer 2

The answer is that

    CMD ["cluster-info","dump"]

Or when there is a space in the kubectl command line, separate it with a comma.