Comment 3 for bug 1934522

This was a known breaking change between 2.8.x and 2.9.x.

I think we can be a bit more clever with this, maybe consider the controller as well, but in reality, this is known and documented clearly when 2.9.x was released.

See "Architecture and series constraint selection for charms" from https://discourse.charmhub.io/t/juju-2-9-0-release-notes/4525 and "Architecture" from https://discourse.charmhub.io/t/charmhub/3991 (there are more documentation that I've added).

So I believe we've let people know here.