auto-upgrading models

[Eric Snow]

In a recent bug I was working on the issue of auto-upgrading models
came up.  I also ran into this personally not too long ago.
Currently, running "juju upgrade-juju -m admin --upload-tools"[1]
upgrades the admin model to a new version.  To set the version of any
other model to the uploaded one, you must do so separately afterward,
e.g. "juju upgrade-juju -m default 2.0-rc1.3". [2]

The fact that you must upgrade the non-admin model separately is
something new with multi-model support.  Perhaps it is only something
that will throw off folks that have relied on --upload-tools
previously and perhaps it is something that we'll just adjust to.
However, I wanted to bring the matter up here and identify potential
courses of action (not all mutually exclusive):

1. do nothing (rely on users to know to always upgrade juju per-model)
2. clearly point this out in the documentation
3. add a note in the output of "juju upgrade-juju --upload-tools"
reminding admins to manually upgrade each model
4. make the "juju is out-of-date" warnings also show up for models
relative to the controller
5. auto-upgrade models when the controller is upgraded
6. auto-upgrade but have a flag to not auto-upgrade
7. have a flag to auto-upgrade

FWIW, I don't consider #1 or #5 to be acceptable options.  I'm on the
fence about #6; it aligns with what I expect would be a better default
experience but hesitate to make unrequested changes of that sort by
default.  So #7 might be more appropriate if the consequences of #6
would be too risky.  Regardless, I do think the user experience of
upgrade-juju could be improved.

Thoughts?

-eric


[1] You can no longer upload tools to any other model than admin.
[2] Thankfully, due to some recent work by axw the new version is
*available* to all models.