remote endpoint offer will not leave model

[james beedy]

I have a model in which I cannot remove the remote offer. Subsequently, I cannot migrate the model due to the stuck offer/remote relation.

See https://paste.ubuntu.com/p/8qXPVqY6Yw/

[Richard Harding (rharding)]

Hmm, it seems like we should be able to check/migrate models with a remote offer. Asking Ian to take a peek and see if this is a known limitation and how we make sure we have a smooth path here.

[Ian Booth (wallyworld)]

@rharding by design we do not support migrating models with offers because it would disrupt any consumers that may be using the offer. We could possibly allow migration if there are no consumers but that would also require locking down the offer in which case it was considered easiest just to remove the offer first and re-create after migration

We also don't support migrating models with consumed applications due to all the messy firewall and ingress network implications on the offering model.

The issue here though appears to be that there's a consumed application (not an offer) where the application on the offering side has stopped. In this case removing the terminated SAAS application should be sufficient.

[Joseph Phillips (manadart)]

Prior changes added the ability to force remove an offer, but now on the edge branch we can successfully migrate models with CMR offers consumed externally, and have the relations maintained.

At the moment, this is only works on controllers bootstrapped with a feature flag enabled via:
export JUJU_DEV_FEATURE_FLAGS=cmr-migrations

We're going to ensure that we can migrate consumers of CMRs, then at some point the feature flag will be removed. We will *probably* then backport it all for a 2.7 point release.