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

[Launchpad Bug Tracker]

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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

** Affects: cloud-archive
     Importance: Undecided
         Status: New

** Affects: cloud-archive/epoxy
     Importance: Undecided
         Status: New

** Affects: watcher (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: watcher (Ubuntu Noble)
     Importance: Undecided
         Status: New

** Affects: watcher (Ubuntu Plucky)
     Importance: Undecided
         Status: New

** Affects: watcher (Ubuntu Questing)
     Importance: Undecided
         Status: New


** Tags: patch
-- 
[SRU] Backport feature for disabling migration to Noble and Plucky
https://bugs.launchpad.net/bugs/2122551
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