Set Instance AZ from Selection AZ during build reschedule

This builds on change Ia50c5f4dd2204f1cafa669097d1e744479c4d8c8
to use the Selection.availability_zone value when rescheduling
during initial server create so that the cell conductor does not
have to make an up-call to the aggregates table in the API DB
which will fail if the cell conductor is not configured to use
the API DB.

The functional test added in I62179d6b93ea1a23c4906477ee19b422bfcb72a2
is updated to show the failure is gone and we get the AZ from the
Selection object during the reschedule.

For the case that the availability_zone field is not in the Selection
object, test_build_reschedule_get_az_error still covers that.

Change-Id: I1f1c25cb4de924a1d6c3a979b758efd736bdbff0
Partial-Bug: #1781286

nova/conductor/manager.py

@@ -745,17 +745,22 @@ class ComputeTaskManager(base.Base):
                         requested_networks)
                     return
 
-            try:
-                instance.availability_zone = (
-                    availability_zones.get_host_availability_zone(context,
-                            host.service_host))
-            except Exception as exc:
-                # Put the instance into ERROR state, set task_state to None,
-                # inject a fault, etc.
-                self._cleanup_when_reschedule_fails(
-                    context, instance, exc, legacy_request_spec,
-                    requested_networks)
-                continue
+            # The availability_zone field was added in v1.1 of the Selection
+            # object so make sure to handle the case where it is missing.
+            if 'availability_zone' in host:
+                instance.availability_zone = host.availability_zone
+            else:
+                try:
+                    instance.availability_zone = (
+                        availability_zones.get_host_availability_zone(context,
+                                host.service_host))
+                except Exception as exc:
+                    # Put the instance into ERROR state, set task_state to
+                    # None, inject a fault, etc.
+                    self._cleanup_when_reschedule_fails(
+                        context, instance, exc, legacy_request_spec,
+                        requested_networks)
+                    continue
 
             try:
                 # NOTE(danms): This saves the az change above, refreshes our

nova/tests/functional/regressions/test_bug_1781286.py

@@ -11,6 +11,7 @@
 # under the License.
 
 import fixtures
+import mock
 from oslo_db import exception as oslo_db_exc
 
 from nova.compute import manager as compute_manager
@@ -56,6 +57,7 @@ class RescheduleBuildAvailabilityZoneUpCall(
         self.addCleanup(fake_notifier.reset)
 
     def test_server_create_reschedule_blocked_az_up_call(self):
+        self.flags(default_availability_zone='us-central')
         # We need to stub out the call to get_host_availability_zone to blow
         # up once we have gone to the compute service. With the way our
         # RPC/DB fixtures are setup it's non-trivial to try and separate a
@@ -78,22 +80,19 @@ class RescheduleBuildAvailabilityZoneUpCall(
         server = self._build_minimal_create_server_request(
             self.api, 'test_server_create_reschedule_blocked_az_up_call')
         server = self.api.post_server({'server': server})
-        # FIXME(mriedem): This is bug 1781286 where we reschedule from the
-        # first failed host to conductor which will try to get the AZ for the
-        # alternate host selection which will fail since it cannot access the
-        # API DB.
-        # Note that we have to wait for the notification before calling the API
-        # to avoid a race where instance.host is not None and the API tries to
-        # hit the AggregateList.get_by_host method we mocked to fail.
-        fake_notifier.wait_for_versioned_notifications(
-            'compute_task.build_instances.error')
-        server = self._wait_for_server_parameter(
-            self.api, server, {'status': 'ERROR',
-                               'OS-EXT-SRV-ATTR:host': None,
-                               'OS-EXT-STS:task_state': None})
-        # Assert there is a fault injected on the server for the error we
-        # expect.
-        self.assertIn('CantStartEngineError', server['fault']['message'])
+        # Because we poisoned AggregateList.get_by_host after hitting the
+        # compute service we have to wait for the notification that the build
+        # is complete and then stop the mock so we can use the API again.
+        fake_notifier.wait_for_versioned_notifications('instance.create.end')
+        # Note that we use stopall here because we actually called
+        # build_and_run_instance twice so we have more than one instance of
+        # the mock that needs to be stopped.
+        mock.patch.stopall()
+        server = self._wait_for_state_change(self.api, server, 'ACTIVE')
+        # We should have rescheduled and the instance AZ should be set from the
+        # Selection object. Since neither compute host is in an AZ, the server
+        # is in the default AZ from config.
+        self.assertEqual('us-central', server['OS-EXT-AZ:availability_zone'])
 
 
 class RescheduleMigrateAvailabilityZoneUpCall(