Since dockershim has been deprecated and soon (as of kubernetes 1.22+) to be
removed, there is a need to migrate cluster container-runtime to some other CRI
compatible container runtime. At the moment KubeOne supports only containerd as
a second option.
The cluster is divided into 3 groups of nodes:
- control-plane nodes
- static workers
- dynamic workers
and each one needs to be migrated.
Please be aware that this operation is quite violent on the cluster as
containers on control-plane and static-worker nodes will be stopped and
All kubernetes versions prior 1.22+ (where switch will happen) have to
explicitly specify the containerd as a container runtime in the config.
For this please use
containerRuntime.containerd field as shown below.
Migrate control-plane and static-workers
Once the config is set to containerd:
terraform output -json > tf.json
kubeone migrate to-containerd -t tf.json
This step will do the following on each control-plane and static-worker node:
- reconfigure kubelet to communicate over CRI to containerd
- reconfigure containerd to enable CRI plugin
- stop ALL docker containers
- remove ALL docker containers
- restart kubelet
- wait (with 10 minutes timeout) for all containers to became ready on give node
Once previous step is completed, machine-controller deployment will be
-container-runtime=containerd flag. But your existing
dynamic-workers still using docker. In order to get rid of docker in
dynamic-workers you need to rolling recreate dynamic-workers. To do that please
force machine-controller to recreate Machines. This can be done by patching
MachineDeployment objects at
spec.template.metadata.annotations for example.
See more at Rolling Restart MachineDeploments
If you wish to, it’s now safe to uninstall docker / docker-cli. Dockerd is still
running in your control-plane and static-workers nodes, it’s just kubelet now
configured to not use it anymore.
Do not just disable docker, but uninstall it if you wish to get rid of docker!
systemctl disable --now docker IS NOT ENOUGH, you will have to leave
it running or uninstall completely!