[wishlist] Config item for a private registry with credentials

[Xav Paice]

Currently, there's a relation available for the docker-registry charm should we wish to use a private registry. However, we have a case where there's already a private registry outside the environment, and it needs credentials. We currently have no way to inject that information to the Kubernetes workers, and so the registry cannot be used.

Sort of related: https://bugs.launchpad.net/charm-kubernetes-worker/+bug/1831153

[Tim Van Steenburgh (tvansteenburgh)]

Pretty sure this is possible, but we need to make sure it's documented. Docs need to cover the following scenarios:

- pre 1.15 configuration with docker
- post 1.15 configuration with docker
- post 1.15 configuration with containerd

[Chris Johnston (cjohnston)]

I believe this is possible now in containerd and Docker.

[George Kraft (cynerva)]

Yep, thanks for pointing it out. This is possible with the custom_registries config for containerd[1] and the docker-logins config for docker[2].

[1]: https://ubuntu.com/kubernetes/docs/1.19/charm-containerd#custom_registries-description
[2]: https://ubuntu.com/kubernetes/docs/1.19/charm-docker#docker-logins-description