[Bug 2074309] Re: upgrade 22.04 -> 24.04 won't start due to feature flags

[kelv]

@michdz and @ahasenack thank you very much.

Separately, perhaps this is the right place to discuss the plan for
RabbitMQ packages in Ubuntu moving forward. This will likely be an issue
again in 1.5 years when the next LTS drops.

As mentioned by the RabbitMQ team in [this discussion raised by michdz
earlier](https://github.com/rabbitmq/rabbitmq-server/discussions/11938),
the release cadence of RabbitMQ currently does not align with Ubuntu LTS
support timelines. To avoid similar issues in the future, it might be
necessary to include these intermediate RabbitMQ releases so that users
can upgrade seamlessly, or alternatively, direct users to the RabbitMQ
managed repository.

While I applaud the ingenuity of the Podman workaround suggested by some
members, users need to test feature flags first (this is why RabbitMQ
itself does not enable feature flags automatically). Given that testing
is necessary, it seems the only viable solution is to provide users with
the intermediate packages, enabling them to upgrade incrementally.

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https://bugs.launchpad.net/bugs/2074309

Title:
  upgrade 22.04 -> 24.04 won't start due to feature flags

Status in Release Notes for Ubuntu:
  New
Status in rabbitmq-server package in Ubuntu:
  Confirmed
Status in ubuntu-release-upgrader package in Ubuntu:
  Invalid
Status in rabbitmq-server source package in Noble:
  Confirmed
Status in ubuntu-release-upgrader source package in Noble:
  Fix Released
Status in rabbitmq-server source package in Oracular:
  Confirmed
Status in ubuntu-release-upgrader source package in Oracular:
  Invalid

Bug description:
  [Impact]

  Upgrading systems with rabbitmq-server installed will leave the server
  in a bad state because upgrading directly from the version in Jammy to
  the version in Noble is not supported by upstream rabbitmq-server.

  [Test Plan]

  For now, we add an upgrade quirk to prevent upgrades from Jammy to
  Noble if rabbitmq-server is installed, and provide an brief
  explanation to the user.

  To test:

  1. Create a Jammy container

  $ lxc launch ubuntu:jammy jammy

  2. Install rabbitmq-server

  $ apt install -y rabbitmq-server

  3. Attempt the upgrade

  $ do-release-upgrade -d

  The upgrade should abort with a message explaining why.

  [Impact]

  This quirk uses a common pattern in ubuntu-release-upgrader for
  similar purposes. If the package name was typo'd, it would not work
  correctly.

  [Other information]

  We may eventually need another SRU to revert this change if another
  solution is found.

  [Original Description]

  Hi,

  I was just doing an upgrade from ubuntu 22.04 server to 24.04 server.

  After upgrading, the rabbitmq-server cannot be started anymore.

  Reason:

  See
  https://www.rabbitmq.com/blog/2022/07/20/required-feature-flags-in-rabbitmq-3.11

  Higher versions of rabbitmq require feature flags to be set *before*
  upgrade. In my rabbitmq installation these features had not been set,
  therefore the the rabbitmq server would not start. They ask you to
  downgerade to an earlier version and do the upgrade.

  I therefore used LXD to run a Ubuntu 22.04 machine with rabbitmq 3.9
  to set the missing feature flags and achieved:

  rabbitmqctl  enable_feature_flag all

  rabbitmqctl list_feature_flags
  Listing feature flags ...
  name    state
  implicit_default_bindings       enabled
  maintenance_mode_status enabled
  quorum_queue    enabled
  stream_queue    enabled
  user_limits     enabled
  virtual_host_metadata   enabled

  But it still does not work, it still complains about  one feature
  missing:

  classic_mirrored_queue_version

  unfortunately, this is required by rabbitmq 3.12 coming with Ubuntu
  24.04, but is not known and thus cannot be set by rabbitmq 3.9 coming
  with Ubuntu 22.04.

  Now the problem is: There is no Ubuntu coming with 3.9 or 3.10. Ubuntu
  jumps directly from rabbitmq 3.9 to rabbitmq 3.12, although there is
  no upgrade path from 3.9 to 3.12.

  Three nasty options:

  - loose your data and configuration and run from scratch
  - run an old version in either docker or LXD
  - try some upgrade path with docker/podman and non-ubuntu versions of rabbitmq

  Unfortunately,

  https://hub.docker.com/_/rabbitmq

  does not list versions older than 3.12, but they still seem to be
  available, so this might by some migration/workaround path.

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