docker-logins config information lost on upgrade from 1.14 -> 1.15

[Jay Kuri]

After an upgrade from charmed kubernetes 1.14 to 1.15, and upon adding the docker subordinate, the workers no longer had access to registries they previously had access to.

The issue seems to be that as of 1.15, the source of authority for docker login information is the docker charm, not the kubernetes-worker charm. (And, in fact, the config in kubernetes-worker is ignored)

What I did:

Post 1.14 -> 1.15 upgrade - Attempted to migrate a pod to a new worker.

What I expected:

The pod would start on the new worker, the old worker would be torn down.

What happened instead:

The pod went into ImagePullBackOff because it could not access the client docker images.

Also - existing worker which prior to the upgrade could pull client images could no longer pull them due to auth errors.

Details / Workaround:

The issue seems to be that since we have a docker subordinate in 1.15, the docker-logins data that actually gets used comes from that charm's config... where previously it came from the kubernetes-worker config.

Adding the login information to the docker-logins config on the docker charm resolves the situation.