Running k0s in Docker

We publish a k0s container image with every release. By default, we run both controller and worker in the same container to provide an easy local testing “cluster”.

The containers are published both on Docker Hub and GitHub. The examples in this page show Docker Hub, because it’s more simple to use. Using GitHub requires a separate authentication (not covered here). Alternative links:

  • docker.io/k0sproject/k0s:latest
  • docker.pkg.github.com/k0sproject/k0s/k0s:”version”

You can run your own k0s-in-docker easily with:

  1. docker run -d --name k0s --hostname k0s --privileged -v /var/lib/k0s -p 6443:6443 docker.io/k0sproject/k0s:latest

Just grab the kubeconfig file with docker exec k0s cat /var/lib/k0s/pki/admin.conf and paste e.g. into Lens.

Running workers

If you want to attach multiple workers nodes into the cluster you can run separate containers for each worker.

First, we need a join token for the worker:

  1. token=$(docker exec -t -i k0s k0s token create --role=worker)

Then join a new worker by running the container with:

  1. docker run -d --name k0s-worker1 --hostname k0s-worker1 --privileged -v /var/lib/k0s docker.io/k0sproject/k0s:latest k0s worker $token

Repeat for as many workers you need, and have resources for. :)

Docker Compose

You can also run k0s with Docker Compose:

  1. version: "3.9"
  2. services:
  3.   k0s:
  4.     container_name: k0s
  5.     image: docker.io/k0sproject/k0s:latest
  6.     command: k0s controller --config=/etc/k0s/config.yaml --enable-worker
  7.     hostname: k0s
  8.     privileged: true
  9.     volumes:
  10.       - "/var/lib/k0s"
  11.     tmpfs:
  12.       - /run
  13.       - /var/run
  14.     ports:
  15.       - "6443:6443"
  16.     network_mode: "bridge"
  17.     environment:
  18.       K0S_CONFIG: |-
  19.         apiVersion: k0s.k0sproject.io/v1beta1
  20.         kind: Cluster
  21.         metadata:
  22.           name: k0s
  23.         # Any additional configuration goes here ...

Known limitations

No custom Docker networks

Currently, we cannot run k0s nodes if the containers are configured to use custom networks e.g. with --net my-net. This is caused by the fact that Docker sets up a custom DNS service within the network and that messes up CoreDNS. We know that there are some workarounds possible, but they are bit hackish. And on the other hand, running k0s cluster(s) in bridge network should not cause issues.