Open Stack

Hi all,

So I've recently had several discussions related to $subject.

In summary - there's a requirement to enable underclouds to support
deploying/updating previous versions of OpenStack overclouds.

So, say I upgrade my liberty undercloud to master/mitaka, I'd like to
ensure the following is possible:

1. Maintain any existing (liberty) overcloud without being forced to
immediately upgrade to Mitaka (updating the undercloud can pull in features
required to enable this upgrade however).

2. Deploy a new overcloud, with the choice between either liberty or mitaka

This has some implications related to distributing tripleo-heat-templates
(need to allow for packaging to either install both versions of t-h-t, or
always install all versions via one package), and then there are related
requirements related to tripleoclient (and potentially tripleo-common), so
we maintain backwards compatiblity wrt overcloud deployment/update.

So, some questions:

- Do we actually want stable branches for tripleoclient (or even
  tripleo-common?) if we have to maintain backwards compatibility?

- Can we add features to tripleoclient now, to make it easier to
  pre-configure known locations for specific releases (this should be
  configurable via a config file IMO, not hard-coded)?

- How might we effectively test this in CI?  Have a job which deploys e.g
  a stable/liberty overcloud with a master undercloud?

- How hard would it be to wire in image-building for a previous release
  (Mitaka/master undercloud building liberty overcloud-full) - would it be
  reasonable to assume existing images and say the undercloud only supports
  building images for one release version?

Thoughts and feedback and volunteers appreciated, thanks!

Steve