ERROR application "kubernetes-worker" has no "docker-registry" relation

Following up on the behavior I described in another post, I found on this site that one might need to put
juju relate kubernetes-worker:docker-registry docker-registry:docker-registry. However, this yields error:

ERROR application "kubernetes-worker" has no "docker-registry" relation. Maybe this is the reason why pulling an image from the registry gives me the bad certificate error ?