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