Re: Ceph release cadence

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On 17-09-06 18:23, Sage Weil wrote:
Hi everyone,

Traditionally, we have done a major named "stable" release twice a year,
and every other such release has been an "LTS" release, with fixes
backported for 1-2 years.

With kraken and luminous we missed our schedule by a lot: instead of
releasing in October and April we released in January and August.

A few observations:

- Not a lot of people seem to run the "odd" releases (e.g., infernalis,
kraken).  This limits the value of actually making them.  It also means
that those who *do* run them are running riskier code (fewer users -> more
bugs).

- The more recent requirement that upgrading clusters must make a stop at
each LTS (e.g., hammer -> luminous not supported, must go hammer -> jewel
-> lumninous) has been hugely helpful on the development side by reducing
the amount of cross-version compatibility code to maintain and reducing
the number of upgrade combinations to test.

- When we try to do a time-based "train" release cadence, there always
seems to be some "must-have" thing that delays the release a bit.  This
doesn't happen as much with the odd releases, but it definitely happens
with the LTS releases.  When the next LTS is a year away, it is hard to
suck it up and wait that long.

A couple of options:

* Keep even/odd pattern, and continue being flexible with release dates

   + flexible
   - unpredictable
   - odd releases of dubious value

* Keep even/odd pattern, but force a 'train' model with a more regular
cadence

   + predictable schedule
   - some features will miss the target and be delayed a year

* Drop the odd releases but change nothing else (i.e., 12-month release
cadence)

   + eliminate the confusing odd releases with dubious value
* Drop the odd releases, and aim for a ~9 month cadence. This splits the
difference between the current even/odd pattern we've been doing.

   + eliminate the confusing odd releases with dubious value
   + waiting for the next release isn't quite as bad
   - required upgrades every 9 months instead of ever 12 months

* Drop the odd releases, but relax the "must upgrade through every LTS" to
allow upgrades across 2 versions (e.g., luminous -> mimic or luminous ->
nautilus).  Shorten release cycle (~6-9 months).

   + more flexibility for users
   + downstreams have greater choice in adopting an upstrema release
   - more LTS branches to maintain
   - more upgrade paths to consider

Other options we should consider?  Other thoughts?
What about this:
* drop odd releases
* have ~9 months release schedule
* no version jumping
* bugfix support for 2 release cycles
* list of major incoming features with their status, disabled by feature flag. * have more QA passed dev releases so that people waiting for new features would be able to try them out

This way we trade shorter release cycle with longer bugfix support but no version jumping. This way stable folks could upgrade from "legacy-stable" to "old-stable" having already multiple minor fixes in both releases.

And bleading-edge people waiting for some features would know current status of new features (e.g. multi-active MDS going stable in L was a surprise for me). With dev releases to run in dev/staging env for testing.

Potentially shorter releases would have less features in, so it should be less risky to use them and of course shorter wait before new release.

Thanks!
sage
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