This is a proposal for DM to commit to supporting (perhaps selected) DM stack releases with bugfixes and occasional backports of functionality. The proposal was triggered by a discussion at the Project Science Team meeting last week (incl. Chris Stubbs, Chuck Claver, Zeljko Ivezic and Robert Lupton), but I think the problem's been recognized for a while now. After a little discussion with Kian-Tat Lim and Robert Lupton, I thought that an RFC would be in order.

The issue seems to be that our releases de-facto become outdated very quickly, as bugfixes and new functionality tend to land on master. This makes our downstream users gravitate towards using master (e.g., the sims team), but at a cost of issues with API breakage unrelated to their work and additional instability. This instability propagates far out, as sims codes are becoming used broadly within the LSST community (especially within DESC, and MAF is being used across all collaborations). It also makes the discoverable docs (which may refer to the APIs as they were at the time of the release) inconsistent with what people are actually using (whatever is on master). Finally, it makes it difficult to simultaneously use the DM release and the most recent sims release.

The concrete straw-man proposal (just to begin the discussion) is for us (DM) to commit to:

• Backporting bugfixes to some number of stable releases (likely only the most recent one?)
• Occasional backports of new functionality that may be required by downstream users
• Regularly (at least nightly) CI-ing the backports above
• Making regular (~monthly?) point releases with the backports accumulated above (including binaries, when we get to releasing those)
• Never breaking backwards compatibility in point releases.

If we do this, it should enable our downstream clients (e.g., the sims team) always work off of a stable release, rather than a master. That will make it possible to have DM and sims releases setup-ed (in the EUPS (or conda) sense) at the same time. It will also make support and documentation easier – we can point everyone to the docs related to the release (which we then maintain), rather than have downstream people follow our development process to understand what's going on on master. Finally, if we commit to supporting stable versions it will be easier for other subsystems to use it (e.g., the camera team).

This proposal will obviously require resources (K-T mentioned maintenance engineers), but I'd like to focus the discussion here on what would be a good process to establish here, both from DM's point of view as well as our downstream users (e.g., sims – Lynne Jones or Chris Walter or others, feel free to comment). And given the release of X16 in a few weeks, this discussion is timely!