Comment 23 for bug 1727355

>We could change Juju code to hard code the preferred LTS as one we know works but this means we need to change Juju each time we want to update the preferred LTS.

I strongly prefer an approach where what version of Ubuntu deployed doesn't change on release dates. (similar breakage happened to MAAS in the past https://bugs.launchpad.net/maas/+bug/1573046)

My preference would be if you are on an LTS version of Ubuntu, use that version. If not, use a hardcoded Juju-team preferred version. I'm not sure I'd want stable versions of Juju to ever silently change what they deploy.