Address old TODO in claim_resources_on_destination

The TODO at the end of the method was based on some old
nova-compute behavior which was removed with change
I39d93dbf8552605e34b9f146e3613e6af62a1774 in Rocky.

Instead of logging a warning, ConsumerAllocationRetrievalFailed
is now raised since without the instance consumer allocations
on the source node during a forced evacuate we cannot proceed
with making those allocations on the destination host.

The method is refactored a bit for clarity while in here and
to drop the big nesting.

Remember that this method is *only* called in the case of a
live migration or evacuate operation with a forced target host
and evacuate is the only case where source_allocations are not
provided.

Change-Id: I988d1bd4d7eb1a01d443e3d93964bd09afcc4929

nova/scheduler/utils.py

@@ -529,6 +529,9 @@ def claim_resources_on_destination(
                                      consumer
     """
     # Get the current allocations for the source node and the instance.
+    # NOTE(gibi) For the live migrate case, the caller provided the
+    # allocation that needs to be used on the dest_node along with the
+    # expected consumer_generation of the consumer (which is the instance).
     if not source_allocations:
         # NOTE(gibi): This is the forced evacuate case where the caller did not
         # provide any allocation request. So we ask placement here for the
@@ -544,13 +547,17 @@ def claim_resources_on_destination(
             context, instance.uuid)
         source_allocations = allocations.get('allocations', {})
         consumer_generation = allocations.get('consumer_generation')
-    else:
-        # NOTE(gibi) This is the live migrate case. The caller provided the
-        # allocation that needs to be used on the dest_node along with the
-        # expected consumer_generation of the consumer (which is the instance).
-        pass
 
-    if source_allocations:
+        if not source_allocations:
+            # This shouldn't happen, so just raise an error since we cannot
+            # proceed.
+            raise exception.ConsumerAllocationRetrievalFailed(
+                consumer_uuid=instance.uuid,
+                error=_(
+                    'Expected to find allocations for source node resource '
+                    'provider %s. Retry the operation without forcing a '
+                    'destination host.') % source_node.uuid)
+
     # Generate an allocation request for the destination node.
     # NOTE(gibi): if the source allocation allocates from more than one RP
     # then we need to fail as the dest allocation might also need to be
@@ -603,19 +610,6 @@ def claim_resources_on_destination(
                   {'instance_uuid': instance.uuid,
                    'host': dest_node.host})
         raise exception.NoValidHost(reason=reason)
-    else:
-        # This shouldn't happen, but it could be a case where there are
-        # older (Ocata) computes still so the existing allocations are
-        # getting overwritten by the update_available_resource periodic
-        # task in the compute service.
-        # TODO(mriedem): Make this an error when the auto-heal
-        # compatibility code in the resource tracker is removed.
-        LOG.warning('No instance allocations found for source node '
-                    '%(source)s in Placement. Not creating allocations '
-                    'for destination node %(dest)s and assuming the '
-                    'compute service will heal the allocations.',
-                    {'source': source_node.uuid, 'dest': dest_node.uuid},
-                    instance=instance)
 
 
 def set_vm_state_and_notify(context, instance_uuid, service, method, updates,

nova/tests/unit/scheduler/test_utils.py

@@ -12,6 +12,7 @@
 
 import mock
 from oslo_utils.fixture import uuidsentinel as uuids
+import six
 
 from nova import context as nova_context
 from nova import exception
@@ -759,10 +760,15 @@ class TestUtils(test.NoDBTestCase):
                            'claim_resources',
                            new_callable=mock.NonCallableMock)
         def test(mock_claim, mock_get_allocs):
-            utils.claim_resources_on_destination(
+            ex = self.assertRaises(
+                exception.ConsumerAllocationRetrievalFailed,
+                utils.claim_resources_on_destination,
                 self.context, reportclient, instance, source_node, dest_node)
             mock_get_allocs.assert_called_once_with(
                 self.context, instance.uuid)
+            self.assertIn(
+                'Expected to find allocations for source node resource '
+                'provider %s' % source_node.uuid, six.text_type(ex))
 
         test()