Kubernetes and Docker - Tips and tricks

Posted on January 29th, 2019

Kubernetes / k8s

Get a shell to the running Container running in kubenetes with kubectl

  • kubectl exec -it shell-demo-id -- /bin/bash

How to map file istead of directory from a configmap with volumenMounts

Mount a file from a configmap certificate.service.pfx to /app/certificate.service.pfx.

  • Once you mount a volume(no matter if it's a configmap or others), it overrides the mountPath with the key in the config map as files.
  • We then need to specify that we only want one of the keys in the ConfigMap. In this way, the original content in /app folders won't be affected.
  • This is there the subPath comes in. We need to tell the volume mounts to use a subpath from our configmap.
  • This now means that the mountPath is actually getting mounted as a single file instead of a directory named: certificate.service.pfx with all the keys in the configmap in it.
  • Below you can see the yaml for it.


    - name: certificate-config
      mountPath: /app/certificate.service.pfx
      subPath: certificate.service.pfx
 - name: certificate-config
     name: certificate-configmap


Install utils in a running docker image

When working with Docker often is uses a very clean linux distro. I often use microsoft/dotnet - both sdk and runetime ... but they don't come with either "ping" or "wget" commands with can be usefull in debug scenarios.

To install the "ping" command use the following when you have a shell for the running container:

  • apt-get update
  • apt-get install iputils-ping

You should now be able to use the ping command. The same goes for "wget" ... just use apt-get install wget instead.

To clear running containers:

docker rm -f $(docker ps -a -q)

To clear build images

docker rmi -f $(docker images -a -q)

To clear volumes:

docker volume rm $(docker volume ls -q)

This command let you explore a docker image:

docker run --rm -it --entrypoint=/bin/bash name-of-image