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[Avocado-devel] [RFC v2]: Avocado maintainability and integration with avocado-vt (was: "Avocado supportability and integration with avocado-vt)



Hi Folks.

This RFC contains proposals and clarifications regarding the
maintenance and release processes of Avocado.

We understand there are multiple teams currently depending on the
stability of Avocado and we don't want their work to be disrupted
by incompatibilities or instability in new releases.

TL;DR:

  We plan to keep the current approach of sprint releases every
  3-4 weeks, but we're introducing "Long Term Stability" releases
  which should be adopted in production environments where users
  can't keep up with frequent upgrades.


Changes from v1:
  - Changed "Support" to "Stability" and "supported" to
    "maintained" [Jeff Nelson]
  - Misc improvements and clarifications in the
    supportability/stability statements [Jeff Nelson, me]
  - Fixed a few typos [Jeff Nelson, me]


Introduction
--------------

We make new releases of Avocado every 3-4 weeks on average.  In
theory at least, we're very careful with backwards compatibility.
We test Avocado for regressions and we try to document any
issues, so upgrading to a new version should be (again, in
theory) safe.

But we know in practice things have to change during development
and regressions are introduced by accident, thus frustrating more
conservative users. We also understand it's not feasible for
users to upgrade Avocado very frequently in a production
environment.

The objective of this RFC is to clarify our maintenance practices
and introduce Long Term Stability (LTS) releases, which are
intended to solve, or at least mitigate, these problems.


Our definition of maintained, or stable
---------------------------------------

First of all, Avocado and its sub-projects are provided 'AS IS'
and WITHOUT ANY WARRANTY, as described in the LICENSE file.

The process described here doesn't imply any commitments or
promises. It's just a set of best practices and recommendations.

When something is identified as "stable" or "maintained", it
means the development community makes a conscious effort to keep
it working and consider reports of bugs and issues as high
priorities.  Fixes submitted for these issues will also be
considered high priorities, although they will be accepted only
if they pass the general acceptance criteria for new
contributions (design, quality, documentation, testing, etc),
at the development team discretion.


Maintained projects and platforms
---------------------------------

The only maintained project as of today is the Avocado Test
Runner, including its APIs and core plugins (the contents of
the main avocado git repository).

Other projects kept under the "Avocado Umbrella" in github may be
maintained by different teams (e.g.: avocado-vt) or be considered
experimental (e.g.: avocado-server and avocado-virt).

More about avocado-vt in its own section further down.

As a general rule, fixes and bug reports for Avocado when running
in any modern Linux distribution are welcome.

But given the limited capacity of the development team, packaged
versions of Avocado will be tested and maintained only for the
following Linux distributions:

  * RHEL 7.x (latest)
  * RHEL 6.x (latest)
  * Fedora (stable releases from the Fedora projects)

Ditto for hardware platforms. The development team will maintain:
  * x86
  * ppc64
  * ppc64le

Contributions from the community to maintain other platforms and
operating systems are very welcome.

The lists above may change without prior notice.


Avocado Releases
----------------

The proposal is to have two different types of Avocado releases:

1. Sprint Releases:
  (This is the model we currently adopt in Avocado)
  
  They happen every 3-4 weeks (the schedule is not fixed) and
  their versions are numbered serially, with decimal digits in
  the format <major>.<minor>.  Examples: 33.0, 34.0, 35.0.  Minor
  releases are rare, but necessary to correct some major issue
  with the original release (33.1, 33.2, etc).

  Only the latest Sprint Release is maintained.

  In Sprint Releases we make a conscious effort to keep backwards
  compatibility with the previous version (APIs and behavior) and
  as a general rule and best practice, incompatible changes in
  Sprint Releases should be documented in the release notes and
  if possible deprecated slowly, to give users time to adapt
  their environments.

  But we understand changes are inevitable as the software
  evolves and therefore there's no absolute promise for API and
  behavioral stability.

2. Long Term Stability (LTS) Releases:

  LTS releases should happen whenever the team feels the code is
  stable enough to be maintained for a longer period of time,
  ideally once or twice per year (no fixed schedule).
  
  They should be versioned just like Sprint Releases, but have a
  suffix 'lts' added to them. Examples: 35.0lts, 36.1lts, etc.

  They should be maintained for 18 months, receiving fixes for
  major bugs in the form of minor (sub-)releases. With the
  exception of these fixes, no API or behavior should change in a
  minor LTS release.  In practice each major LTS release will
  imply in the creation of a git branch where only serious issues
  affecting users will be fixed. The code in a LTS branch is
  stable, frozen for new features.

  Notice that although within a LTS release there's a expectation
  of stability because the code is frozen, different (major) LTS
  releases may include changes in behavior, API incompatibilities
  and new features. The development team will make a considerable
  effort to minimize and properly document these changes (changes
  when comparing it to the last major LTS release).

  Sprint Releases are replaced by LTS releases. I.e., in the
  cycle when 35.0lts is released, that's also the version used as
  a Sprint Release (there's no 35.0 -- non lts -- in this case).

  New LTS releases should be done carefully, with ample time for
  announcements, testing and documentation.  It's recommended
  that one or two sprints are dedicated as preparations for a LTS
  release, with a Sprint Release serving as a "LTS beta" release.

  Similarly, there should be announcements about the end-of-life
  (EOL) of a LTS release once it approaches its 18 months of
  life.
 

Misc details
------------

Sprint and LTS releases, when packaged, should be preferably
distributed through different package channels (repositories).
Users can opt to follow whatever channel they prefer. The actual
layout of the packages repositories has not been specified yet.

Via pip, Avocado Sprint Releases will be made available.

The existence of LTS releases should never be used as an excuse
to break a Sprint Release or to introduce gratuitous
incompatibilities there. In other words, Sprint Releases should
still be taken seriously, just as they are today.


Timeline example
----------------

For simplicity, assume each sprint is taking 1 month. The number
of LTS releases is exaggerated to show how they would co-exist
before EOL.

    sprint release 33.0
    sprint release 34.0
      --> start preparing a LTS release, so 35.0 is a beta LTS
    sprint release 35.0
    LTS release 36.0lts (36lts branch is created)
      --> major bug is found, fix gets added to master and to
          the 36lts branch
      --> minor releases are made whenever the development team
          feels it's convenient to do so.
    sprint release 37.0 + 36.1lts # not necessarily in sync
    sprint release 38.0
      --> major bug is found, fix gets added to master and
          36lts branches
      --> minor releases are made whenever the development team
          feels it's convenient to do so.
    sprint release 39.0 + LTS 36.2lts # not necessarily in sync
    sprint release 40.0
    sprint release 41.0
       --> start preparing a LTS release, so 42.0 is a beta LTS
    sprint release 42.0
       --> review and document all compatibility changes
           and features introduced since 36.2lts
    LTS release 43.0lts (43lts branch is created)
    sprint release 44.0
    sprint release 45.0
      --> major bug is found, fix gets added to master and LTS
          branches 36lts and 43lts (if the bug affects users
          there)
      --> minor releases are made whenever the development team
          feels it's convenient to do so.
    sprint release 46.0 + LTS 36.3lts + LTS 43.1lts ...
    sprint release 47.0
    sprint release 48.0
       --> start preparing a LTS release, so 49.0 is a beta LTS
    sprint release 49.0
       --> review and document all compatibility changes and
           features introduced since 43.1lts
    sprint release 50.0lts (50lts branch is created)
       --> EOL for 36lts is approaching, there should be
           some sort of announcement.
    sprint release 51.0
    sprint release 52.0
    sprint release 53.0
    sprint release 54.0
       --> EOL for 36lts (18 months since the release of 36.0lts)
    sprint release 55.0
    ...


avocado-vt
----------

avocado-vt is an Avocado plugin that allows "VT tests" to be run
inside Avocado.  It's a third-party project maintained mostly by
Engineers from Red Hat QE with assistance from the Avocado team
and other community members.

It's a general consensus that QE teams use avocado-vt directly
from git, usually following the master branch, which they
control.

There's no official maintenance or stability statement for
avocado-vt.  Even though the upstream community is quite
friendly and open to both contributions and bug reports,
avocado-vt is made available without any promises for
compatibility or supportability.

When packaged and versioned, avocado-vt rpms should be considered
just snapshots, available in packaged form as a convenience to
users outside of the avocado-vt development community.  Again,
they are made available without any promises of compatibility or
stability.

* Which Avocado version should be used by avocado-vt?

  This is up to the avocado-vt community to decide, but the
  current consensus is that to guarantee some stability in
  production environments, avocado-vt should stick to a specific
  LTS release of Avocado. In other words, the Avocado team
  recommends production users of avocado-vt not to install Avocado
  from its master branch or upgrade it from Sprint Releases.
  
  Given each LTS release will be maintained for 18 months, it
  should be reasonable to expect avocado-vt to upgrade to a new
  LTS release once a year or so. This process will be done with
  support from the Avocado team to avoid disruptions, with proper
  coordination via the avocado mailing lists.

  In practice the Avocado development team will keep watching
  avocado-vt to detect and document incompatibilities, so when
  the time comes to do an upgrade in production, it's expected
  that it should happen smoothly.

* Will it be possible to use the latest Avocado and avocado-vt
  together?

  Users are welcome to *try* this combination.  The Avocado
  development team itself will probably do it internally as a way
  to monitor incompatibilities and regressions.
  
  Given the open source nature of both projects, we expect
  volunteers to step up and maintain an upstream branch of
  avocado-vt that works with the most recent Avocado Sprint
  Release.

  If no volunteers show up, we might release snapshots of
  avocado-vt in the Avocado LTS channel, for convenience only,
  just as we do today with our Sprint Releases.

Thanks.
   - Ademar

-- 
Ademar Reis
Red Hat

^[:wq!


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