support docker registry in containerd deployments

[Kevin W Monroe]

When docker-registry is related to k8s charms, assumptions are made about what client configuration needs to be done. This includes things like "insecure registry" config in docker's daemon.json or running "docker login" for registries that require auth.

This doesn't make sense in a containerd environment where config and client applications like 'docker' may not even be present.

We should conditionally determine which container runtime is present and take appropriate action when a docker-registry is related to either docker- or containerd-based k8s deployments.

[Kevin W Monroe (kwmonroe)]

Targeting k8s-worker, though I think the fix will actually need to be make in https://github.com/charmed-kubernetes/layer-kubernetes-master-worker-base/

[Joseph Borg (joeborg)]

https://github.com/charmed-kubernetes/charm-containerd/pull/13

[George Kraft (cynerva)]

Joe, I had to dig a fair bit to find all the relevant PRs for this issue. In the future, please link all relevant/necessary PRs in the issue.

https://github.com/charmed-kubernetes/charm-docker/pull/8
https://github.com/charmed-kubernetes/layer-kubernetes-master-worker-base/pull/7
https://github.com/charmed-kubernetes/layer-container-runtime-common/pull/2
https://github.com/charmed-kubernetes/layer-container-runtime-common/pull/3
https://github.com/charmed-kubernetes/charm-docker/pull/9
https://github.com/charmed-kubernetes/charm-containerd/pull/13

Please let me know if I missed any.

[George Kraft (cynerva)]

I'm going to recommend that we do not release this as part of 1.15+ck1. The fixes involve removing the docker-registry relations from kubernetes-master and kubernetes-worker, and adding them to the docker and containerd subordinate charms instead. I don't think it makes sense for us to ship something that changes the relations like this as part of a bug fix release unless there is a strong need for it.

[Tim Van Steenburgh (tvansteenburgh)]

+1 George, will move to 1.16, thanks for looking.