** Description changed:
Description:
When performing a cold migration, if an exception is raised by the
driver during confirm_migration (this runs in the source node), the
migration record is stuck in "confirming" state and the allocations
against the source node are not removed.
The instance is fine at the destination in this stage, but the source
host has allocations that is not possible to clean without going to the
database or invoking the Placement API via curl. After several migration
attempts that fail in the same spot, the source node is filled with
these allocations that prevent new instances from being created or
instances migrated to this node.
When confirm_migration fails in this stage, the migrating instance can
be saved through a hard reboot or a reset state to active.
Steps to reproduce:
Unfortunately, I don't have logs of the real root cause of the problem
inside driver.confirm_migration running libvirt driver. However, the
stale allocations and migration status problem can be easily reproduced
by raising an exception in libvirt driver's confirm_migration method,
and it would affect any driver.
Expected results:
Discussed this issue with efried and mriedem over #openstack-nova on
March 25th, 2019. They confirmed that allocations not being cleared up
is a bug.
Actual results:
Instance is fine at the destination after a reset-state. Source node has
stale allocations that prevent new instances from being created/migrated
to the source node. Migration record is stuck in "confirming" state.
Environment:
I verified this bug on on pike, queens and stein branches. Running
libvirt KVM driver.
+
+ =======================================================================
[Impact]
If users attempting to perform cold migrations face any issues when
the virt driver is running the "Confirm Migration" step, the failure leaves
stale allocation records in the database, in migration records in "confirming"
state. The stale allocations are not cleaned up by nova, consuming the user's
quota indefinitely.
This bug was confirmed from pike to stein release, and a fix was
implemented for queens, rocky and stein. It should be backported to
those releases to prevent the issue from reoccurring.
This fix prevents new stale allocations being left over, by cleaning
them up immediately when the failures occur. At the moment, the users
affected by this bug have to clean their previous stale allocations
manually.
[Test Case]
The root cause for this problem may vary for each driver and
environment, so to reproduce the bug, it is necessary first to inject a
failure in the driver's confirm_migration method to cause an exception
to be raised.
An example when using libvirt is to add a line:
raise Exception("TEST")
in
https://github.com/openstack/nova/blob/a57b990c6bffa4c7447081b86573972866c696d2/nova/virt/libvirt/driver.py#L9012
and then restart the nova-compute service.
Then, invoke a cold migration through "openstack server migrate {id}",
wait for VERIFY_RESIZE status, and then invoke "openstack server resize
{id} --confirm". The confirmation will fail asynchronously and the
instance will be in ERROR status, while the migration database record is
in "confirming" state and the stale allocations for the source host is
still present in the "allocations" database table.
[Regression Potential]
New functional test https://review.opendev.org/#/c/657870/ validated the
fix and was backported all the way to Queens. The fix being backported
caused no functional test to fail.
[Other Info]
None
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https://bugs.launchpad.net/bugs/1821594
Title:
[SRU] Error in confirm_migration leaves stale allocations and
'confirming' migration state
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