Comment 16 for bug 1825537

Reviewed: https://review.opendev.org/669361
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=9a977cb28c1c4f2e8d950476fa373326f636dfd6
Submitter: Zuul
Branch: stable/rocky

commit 9a977cb28c1c4f2e8d950476fa373326f636dfd6
Author: Matt Riedemann <email address hidden>
Date: Fri Apr 19 11:54:07 2019 -0400

    Add functional recreate test for regression bug 1825537

    Change I2d9ab06b485f76550dbbff46f79f40ff4c97d12f in Rocky
    (and backported through to Pike) added error handling to
    the resize_instance and finish_resize methods to revert
    allocations in placement when a failure occurs.

    This is OK for resize_instance, which runs on the source
    compute, as long as the instance.host/node values have not
    yet been changed to the dest host/node before RPC casting
    to the finish_resize method on the dest compute. It's OK
    because the instance is still on the source compute and the
    DB says so, so any attempt to recover the instance via hard
    reboot or rebuild will be on the source host.

    This is not OK for finish_resize because if we fail there
    and revert the allocations, the instance host/node values
    are already pointing at the dest compute and by reverting
    the allocations in placement, placement will be incorrectly
    tracking the instance usage with the old flavor against the
    source node resource provider rather than the new flavor
    against the dest node resource provider - where the instance
    is actually running and the nova DB says the instance lives.

    This change adds a simple functional regression test to
    recreate the bug with a multi-host resize. There is already
    a same-host resize functional test marked here which will
    need to be fixed as well.

    Conflicts:
          nova/tests/functional/test_servers.py
          nova/virt/fake.py

    NOTE(mriedem): The test_servers conflict is due to not having
    change If6aa37d9b6b48791e070799ab026c816fda4441c in Rocky. As
    a result, the new regression test also had to be modified for
    the call to assertFlavorMatchesAllocation. The fake module
    conflict is due to not having change
    Iefff121640e04abdbb6a4ae546c447f168dc8af9 in Rocky.

    Change-Id: Ie9e294db7e24d0e3cbe83eee847f0fbfb7478900
    Related-Bug: #1825537
    (cherry picked from commit f4bb67210602914e1b9a678419cf22cfbeaf1431)
    (cherry picked from commit eaa1fc6159ca4437a1e0cbaa77a3da779afb8cb2)