Export Kube Config From Docker Container and Merge

12/03/2022

How to export a kubernetes config context file from inside a docker container, to the host and merge.

Introduction

If you use Docker in Docker (dind) or Kubernetes in Docker (kind) you will end up with a kubectl running inside a docker container but you probably also want to interact using kubectl from localhost.

Export Contexts

Use the docker cp command to copy the kube config file from the container to the localmachine:

docker cp YourContainerName:/UsernameTheContainerIsUsing/.kube/config ./config

For example:

docker cp mycontainer:/root/.kube/config ./config

Ensure the config points to the correct endpoint. Modify the config file and adjust the server field. You might have:

server: https://host.docker.internal:39155

Whereas host.docker.internal won’t resolve from the host machine so that needs to be:

server: https://127.0.0.1:39155

Trial and error is probably required here.

Merge Contexts

Now merge any existing kubectl config file and this new one. The syntax is:

export KUBECONFIG=ExistingFile:NewFile

For example:

export KUBECONFIG=~/.kube/config:~/config

Finally use kubectl to merge and flatten the two configs:

kubectl config view --merge --flatten > ./mergedconfigs && mv ./mergedconfigs ~/.kube/config

Verify that configs are merged:

kubectl config get-contexts

For example:

CURRENT   NAME             CLUSTER          AUTHINFO            NAMESPACE
*         docker-desktop   docker-desktop   docker-desktop      
          k3d-mykeptn      k3d-mykeptn      admin@k3d-mykeptn  

Try It Out

Switch to your new context:

kubectl config use-context k3d-mykeptn

Now try it. From your localhost:

kubectl get ns --context=YourNameContext

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