Handle volume-backed instances in IsolatedHostsFilter

The RequestSpec.image object for a volume-backed instance will
not have the 'id' attribute set because the
nova.utils.get_image_metadata_from_volume() method doesn't convert
the volume['volume_image_metadata']['image_id'] into the ImageMeta.id
field. It is unclear if there are intentional reasons for omitting
this information, but the IsolatedHostsFilter has just never supported
filtering for volume-backed instances based on a provided image id.

The logic within the filter depends on the
restrict_isolated_hosts_to_isolated_images config option, which
defaults to True. When True, a volume-backed instance will not be
put on an isolated host. When False, a volume-backed instance can
go on any host, isolated or not.

Again, it's unclear if we should actually be filtering volume-backed
servers using the image_id from the volume_image_metadata or not,
but it's not what we've historically done so this change simply
fixes the regression bug.

Change-Id: Ieb8abb1a3f04ce008f9617e051e4d720dbe6917a
Closes-Bug: #1746483

nova/scheduler/filters/isolated_hosts_filter.py

@@ -59,7 +59,10 @@ def host_passes(self, host_state, spec_obj):
             return ((not restrict_isolated_hosts_to_isolated_images) or
                    (host_state.host not in isolated_hosts))
 
-        image_ref = spec_obj.image.id if spec_obj.image else None
+        # Check to see if the image id is set since volume-backed instances
+        # can be created without an imageRef in the server create request.
+        image_ref = spec_obj.image.id \
+            if spec_obj.image and 'id' in spec_obj.image else None
         image_isolated = image_ref in isolated_images
         host_isolated = host_state.host in isolated_hosts
 

nova/tests/functional/regressions/test_bug_1746483.py

@@ -92,7 +92,11 @@ def test_boot_from_volume_with_isolated_image(self):
         # networks='none'.
         with utils.temporary_mutation(self.api, microversion='2.37'):
             server = self.api.post_server(server_req_body)
-        server = self._wait_for_state_change(self.api, server, 'ERROR')
-        # Due to bug 1746483 we expect scheduling to fail.
-        self.assertIn("Cannot load 'id' in the base class",
-                      server['fault']['message'])
+        server = self._wait_for_state_change(self.api, server, 'ACTIVE')
+        # NOTE(mriedem): The instance is successfully scheduled but since
+        # the image_id from the volume_image_metadata isn't stored in the
+        # RequestSpec.image.id, and restrict_isolated_hosts_to_isolated_images
+        # is True, the isolated host (host1) is filtered out because the
+        # filter doesn't have enough information to know if the image within
+        # the volume can be used on that host.
+        self.assertEqual('host2', server['OS-EXT-SRV-ATTR:host'])