upgrade-juju should allow downgrading point versions

[Christian Muirhead]

As a fix for https://bugs.launchpad.net/juju/+bug/1732156, upgrade-juju prevents specifying a version lower than the one running on the controller. This is too restrictive - in an ideal world we'd like to allow users to try out a new release and revert to the old one if they find a problem (at least for point releases if it's not feasible for bigger changes).

The reason we don't allow it at the moment is that there is no way to reverse upgrade steps that might have been applied. We could handle this by:
* Allowing a downgrade when there are no upgrade steps that need undoing (combined with a policy of not adding upgrade steps for point releases).
* Allowing a downgrade even if there are upgrade steps when the user specifies --force.
* Actually adding downgrade steps?
* Something else.

More discussion here: https://github.com/juju/juju/pull/8108

[Sandor Zeestraten (szeestraten)]

We'd also really like to see the ability to downgrading or rolling back upgrades.

[Canonical Juju QA Bot (juju-qa-bot)]

This bug has not been updated in 2 years, so we're marking it Low importance. If you believe this is incorrect, please update the importance.