Import model name collision

[kian99]

When working on #1432 to import offers into JIMM, I didn't address the scenario where is collision with an existing offer URL.

For context, an offer URL takes the form:

• [offer-owner]/[model-name].[app-name/alias]
• E.g. admin/foo.postgresql

At first glance it struck me that we can't have a collision when importing offers into JIMM because the Juju controller enforces this URL must be unique. This was until I realised JIMM could import models with the same name from multiple controllers.

Consider Controller A with model foo and Controller B with model foo, both created by an admin user. When importing these models into JIMM, you would import these to a new owner say "kian@canonical.com" the second model import will fail because kian@canonical.com/foo already exists.

Overall, the case where offer URLs collide seems to be a subset of the problem where model names collide.

In #1272 I changed the way model uniqueness was enforced in JIMM. Previously a model was unique according to a combination of (controller, name, owner). Now it is unique according to (name, owner), meaning that we more closely match Juju's behaviour that a user cannot have two models with the same name (previously we had conflicts in the Juju CLI if you had access to two models with the same owner and same model name).

How can we address the situation where you want to import a model where the name is already used because of another controller?
Some ideas:

• Allow the model name to be changed.
• Tell the user to add the model to a different owner.

[ale8k]

What happens if I create:

• Controller A
• Controller B

And on both controllers, create:

• my-model (On A)
• my-model (On B)

And finally, I run:

• juju switch controller-a:my-model
• juju migrate my-model controller-b

I imagine the result of this is the behaviour we want here.

[ale8k]

Tested this, same issue in Juju:

❯ jj migrate my-model controller-b
ERROR target prechecks failed: migration target prechecks failed: model named "my-model" already exists

Closing issue.

[alesstimec]

I think this is still a valid issue: we need to discuss it as a team.

[kian99]

After some more thought on this yesterday, the issue with model names colliding is potentially simply solved by using a different owner (as mentioned above). But application offer URLs can still collide with no way for resolution. I'll change the name of the issue to better reflect this new issue.

Consider:

• Controller A with model foo and Controller B with model foo, both created by an admin user.
• Both models have an application called postgresql.
• When attempting to import these models into JIMM (even using different owners), both will have the same offer URL of admin/foo.postgresql.

Some ideas on solving this:

• Alias the application offer in JIMM, i.e. if an offer URL already exists during import then save the URL with a number attached like admin/foo.postgresql-1.
• Allow the user to provide a "suffix" so they can make their model's offer URLs more unique. I.e. --offer-alias=my-team aliasing the offer to admin/foo.postgresql-my-team.