Discussion: expand etcd_deployment_type: kubeadm to eventually replace etcd_deployment_type: docker

[VannTen]

docker and kubeadm for etcd_deployment_type covers essentially the same goal: running etcd inside a container.

Right now, the kubeadm method is limited to run etcd on control-plane nodes (at least, according to the docs). However, I don't think there is any inherent blockers that prevent running on separate nodes, since kubelet can run standalone, without being part of the cluster.

The endgoal would be deprecating the docker option.

The expected benefits would be:

• kubeadm choice becomes a replacement for docker, but with any container engine of the user choice
• Since we already configure container_manager + kubelet, I don't expect this would add much code to kubespray, and we could get rid of the code managing the docker case + the hard dependency on docker.

This would need 3/4 steps:

• make kubeadm feature equivalent with docker
• provide a migration path (potentially, with manual steps) -> the underlying data is not different, so while this might be tricky, it's doable
• deprecate docker choice (Check usage of deprecated/removed variable in a dedicated role at playbook start. #11039 would help there ...)
• after X releases (minor releases, aka 2.25 -> 2.26) remove docker choice -> with X >= 3 probably.

Wdyt ?

/kind feature
/kind cleanup

[tico88612]

Based on your description in #11039, the plan seems to deprecate the etcd_deployment_type variable itself rather than just the docker option of the etcd_deployment_type. I'm not sure if I understand correctly?

But shouldn't the etcd_deployment_type variable be deprecated?

[VannTen]

Nope, only the `docker` choice. I mentioned #11039 because this kind of stuff is a good usecase for it.