Juju must not allow upgrading from 2.9.x to 3.0.x

[Juan M. Tirado]

Until Juju has a tested functionality to upgrade controllers from 2.9.x to 3.0.x (probably in 3.0.1), the upgrade process must be disabled. This is working as expected right now using clients 2.9.35 and 3.0-rc1 (I have not tested more versions). However, users can by-pass this restriction running:

juju upgrade-controller --agent-version 3.0.0
best version:
    3.0.0
started upgrade to 3.0.0

[Heather Lanigan (hmlanigan)]

also occurs with

$ juju upgrade-controller --build-agent
no prepackaged agent binaries available, using local agent binary 3.0-rc2.1 (built from source)
best version:
    3.0-rc2.1
started upgrade to 3.0-rc2.1

[Heather Lanigan (hmlanigan)]

There was a recent change unrelated change https://github.com/juju/juju/pull/14721 had a small update with new behavior and now:

$ juju version
3.0-rc2-ubuntu-amd64
$ juju status
Model Controller Cloud/Region Version SLA Timestamp
default two-nine localhost/localhost 2.9.35 unsupported 17:58:36Z

Model "admin/default" is empty.
$ juju upgrade-controller
no upgrades available
$ juju upgrade-controller --agent-version 3.0.0
no upgrades available
$ juju upgrade-controller --agent-version 3.0-rc2
no upgrades available

[Heather Lanigan (hmlanigan)]

However:

$ juju upgrade-controller --build-agent
no prepackaged agent binaries available, using local agent binary 3.0-rc2.1 (built from source)
best version:
    3.0-rc2.1
started upgrade to 3.0-rc2.1

[Heather Lanigan (hmlanigan)]

Validation is broken - hidden by a change of MinMajorUpgradeVersion instead of MinMajorMigrateVersion

[Heather Lanigan (hmlanigan)]

Fixing in 2.9, as validation is done in the server only:
https://github.com/juju/juju/pull/14778

[Yang Kelvin Liu (kelvin.liu)]

Some extra fixes for model upgrade/migrate for 3.0: https://github.com/juju/juju/pull/14784