[swift-dev] Proposal for Swift and Ubuntu releases

[Todd Fiala]

Hi all,

I wanted to propose how we can go about handling newer Ubuntu releases in a
systematic way.  This covers how we handle Ubuntu on our CI, but also
reflects where we'll be focusing effort at any given point.  The primary
intent is to support the most recent Ubuntu Long Term Service release and
the absolute latest Ubuntu release, with a bit of overlap when phasing out
the LTS release that is going out of scope.

Since the next release, fast moving or not, is the next Long Term Stability
release, Ubuntu 16.04 LTS (available now), I propose we:

* swap out our 15.10 fast moving release with Ubuntu 16.04 LTS.

* allow 16.04 and 14.04 to co-exist to give our stability-minded community
time to switch over to 16.04.

When 16.10 comes out in October 2016, we drop 14.04 and move 16.10 onto
those builders.

This continues to have us testing against the latest release, which will be
Ubuntu 16.04 LTS when we switch, gives us the latest stable coverage (also
16.04), and gives our community a little more time with active coverage on
14.04, the previous long term support version.  We’ll then get back to the
normal program in October 2016 when we pick up the latest fast-moving
release, with coverage on Ubuntu 16.10 and Ubuntu 16.04 LTS.

This assumes we want to keep our eyes on no more than two Ubuntu releases
at a time, which matches current CI infrastructure planning.

Looking forward over the next two years, this is the schedule I’m proposing:


   - April 2016: Replace Ubuntu 15.10 with Ubuntu 16.04  (coverage: Ubuntu
   14.04, Ubuntu 16.04 LTS)
   - October 2016: Replace Ubuntu 14.04 with Ubuntu 16.10 (coverage: Ubuntu
   16.04 LTS, Ubuntu 16.10)
   - April 2017: Replace Ubuntu 16.10 with Ubuntu 17.04 (coverage: Ubuntu
   16.04 LTS, Ubuntu 17.04)
   - October 2017: Replace Ubuntu 17.04 with Ubuntu 17.10 (coverage: Ubuntu
   16.04 LTS, Ubuntu 17.10)
   - April 2018: Replace Ubuntu 17.10 with Ubuntu 18.04 LTS (coverage:
   Ubuntu 16.04, Ubuntu 18.04 LTS)

Thoughts?  Once we finalize the plan, I'll coordinate with the
infrastructure teams and round up resources needed to get Ubuntu 16.04
supported and on the CI.

Thanks!
Sincerely,
Todd Fiala
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