[Bug 2122551] Re: [SRU] Backport feature for disabling migration to Noble and Plucky

[Quang Ngo]

** Patch added: "lp2122551_uca_epoxy.patch"
   https://bugs.launchpad.net/ubuntu/+source/watcher/+bug/2122551/+attachment/5914487/+files/lp2122551_uca_epoxy.patch

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Title:
  [SRU] Backport feature for disabling migration to Noble and Plucky

Status in Ubuntu Cloud Archive:
  New
Status in Ubuntu Cloud Archive epoxy series:
  New
Status in watcher package in Ubuntu:
  New
Status in watcher source package in Noble:
  New
Status in watcher source package in Plucky:
  New
Status in watcher source package in Questing:
  New

Bug description:
  Watcher upstream has adopted a new feature to the Host Maintenance
  strategy to disable live or cold migration and safely stop active
  instances when migration cannot proceed. This feature is planned for
  Watcher 15.0.0 shipped with OpenStack 25.02, but will be useful if it
  can be backported to Ubuntu Plucky and Noble.

  For example, currently Sunbeam/Canonical OpenStack is mainly using
  Watcher rock images which are pulled from Ubuntu Cloud Archive Epoxy
  (watcher 2:14.0.0) and Caracal (watcher 2:12.0.0). Having this new
  feature will help address this known issue: https://canonical-
  openstack.readthedocs-hosted.com/en/latest/how-
  to/operations/maintenance-mode/#known-issues

  Upstream commit:
  https://opendev.org/openstack/watcher/commit/cc26b3b334e5d60bf04c927c771d572445e4a8bc

  [ Impact ]
   * User problem: Current host maintenance strategy forces migration operations that may not be suitable for all deployment scenarios.

   * Functional Enhancement: Introduces two new input parameters to the Host Maintenance strategy:
    - `disable_live_migration`: When True, forces cold migration instead of live migration
    - `disable_cold_migration`: When True, prevents cold migration of inactive instances
    - Combined usage: When both are True, only stop actions are performed on active instances

   * Backward Compatibility: All changes are additive with sensible
  defaults (both new parameters default to False), ensuring existing
  Host Maintenance strategy deployments continue working unchanged.

   * No API Changes: The feature adds only configuration parameters to
  current schema and internal action handling - no API modifications or
  breaking changes to existing interfaces.

   * Target Releases:
     - Ubuntu 25.04 (Plucky) with watcher 2:14.0.0 -> enables UCA Epoxy
     - Ubuntu 24.04 (Noble) with watcher 2:12.0.0

  [ Test Case ]

   Prerequisite:
    * OpenStack cluster with Watcher enabled.
    * At least two compute nodes in the cluster
    * Test instances running on the maintenance target node

   1. Test Case 1: Backward Compatibility
   # Verify existing behavior is unchanged
   openstack optimize audit create -g cluster_maintaining -s host_maintenance \
     -p maintenance_node=compute01 -p backup_node=compute02

   # Expected: Traditional live/cold migration behavior (no stop actions)
   openstack actionplan show <audit_uuid>

   2. Test Case 2: Both Migrations Disabled
   # Test stop-only behavior (the new stop action)
   openstack optimize audit create -g cluster_maintaining -s host_maintenance \
     -p maintenance_node=compute01 -p disable_live_migration=True \
     -p disable_cold_migration=True

   # Expected: Action plan contains only "stop" actions for instances
   openstack actionplan show <audit_uuid>

   3. Test Case 3: Live Migration Disabled Only
   # Test cold migration fallback
   openstack optimize audit create -g cluster_maintaining -s host_maintenance \
     -p maintenance_node=compute01 -p disable_live_migration=True

   # Expected: Active instances use cold migration, inactive instances use cold migration
   openstack actionplan show <audit_uuid>

   4. Test Case 4: Cold Migration Disabled Only
   # Test live migration with no cold migration
   openstack optimize audit create -g cluster_maintaining -s host_maintenance \
     -p maintenance_node=compute01 -p disable_cold_migration=True

   # Expected: Active instances use live migration, inactive instances remain untouched
   openstack actionplan show <audit_uuid>

  The testing can also be done via Ubuntu OpenStack CI system using
  Tempest to verify the backward compatibility.

  [ Regression Potential / Where problems could occur]

   Configuration Conflicts:
   * Risk: Administrators might misconfigure parameters, leading to unexpected behavior
   * Manifestation: Instances stopped when migration was intended, or vice versa
   * Detection: Review action plans before execution; monitor Watcher logs for parameter validation

   Stop Action Failures:
    * Risk: New stop action might fail on instances with complex configurations (attached volumes, special networking, etc.)
    * Manifestation: Action plan execution failures; instances left in inconsistent states
    * Detection: Failed action plan execution; Nova API errors in Watcher applier logs

   Otherwise, due to no changes in API and the new parameters are set to
  False by default, the regression potential is mitigated with low risk.
  All existing CI jobs in upstream have passed.

  [ Discussion ]
   N/A

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