Disable limit if affinity(anti)/same(different)host is requested

When max_placement_results is less than the total number of nodes in
a deployment it may not be possible to use the affinity, anti-affinity,
same host or different host filters as there is no guarantee
for placement to return the expected hosts under such situations. This
patch disables the max_placement_results parameter when nova queries
placement for ``GET /allocation_candidates`` if the
request_spec.scheduler_hints containts any of group, same_host or
different_host keys.

Note that due to change If7ea02df42d220c5042947efdef4777509492a0b only
being in Train the test in the backport calls resources_from_request_spec
without the context or fake HostManager parameters.

Change-Id: Ia2d5f80b6db59a8f6da03344aeaa6aa599407672
Closes-Bug: #1827628
(cherry picked from commit 2f9e972ba3)

nova/scheduler/utils.py

@@ -491,6 +491,12 @@ def resources_from_request_spec(spec_obj):
     if 'force_nodes' in spec_obj and spec_obj.force_nodes:
         res_req._limit = None
 
+    # Don't limit allocation candidates when using affinity/anti-affinity.
+    if ('scheduler_hints' in spec_obj and any(
+        key in ['group', 'same_host', 'different_host']
+        for key in spec_obj.scheduler_hints)):
+        res_req._limit = None
+
     return res_req
 
 

nova/tests/unit/scheduler/test_utils.py

@@ -10,6 +10,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import ddt
 import mock
 from oslo_utils.fixture import uuidsentinel as uuids
 
@@ -23,6 +24,7 @@ from nova.tests.unit import fake_instance
 from nova.tests.unit.scheduler import fakes
 
 
+@ddt.ddt
 class TestUtils(test.NoDBTestCase):
 
     def setUp(self):
@@ -490,6 +492,42 @@ class TestUtils(test.NoDBTestCase):
                          req.get_request_group(None).resources)
         self.assertEqual(1, len(list(req.resource_groups())))
 
+    @ddt.data(
+        # Test single hint that we are checking for.
+        {'group': [uuids.fake]},
+        # Test hint we care about and some other random hint.
+        {'same_host': [uuids.fake], 'fake-hint': ['fake-value']},
+        # Test multiple hints we are checking for.
+        {'same_host': [uuids.server1], 'different_host': [uuids.server2]})
+    def test_resources_from_request_spec_no_limit_based_on_hint(self, hints):
+        """Tests that there is no limit applied to the
+        GET /allocation_candidates query string if a given scheduler hint
+        is in the request spec.
+        """
+        flavor = objects.Flavor(vcpus=1,
+                                memory_mb=1024,
+                                root_gb=15,
+                                ephemeral_gb=0,
+                                swap=0)
+        fake_spec = objects.RequestSpec(
+            flavor=flavor, scheduler_hints=hints)
+        expected = utils.ResourceRequest()
+        expected._rg_by_id[None] = objects.RequestGroup(
+            use_same_provider=False,
+            resources={
+                'VCPU': 1,
+                'MEMORY_MB': 1024,
+                'DISK_GB': 15,
+            },
+        )
+        expected._limit = None
+        resources = utils.resources_from_request_spec(fake_spec)
+        self.assertResourceRequestsEqual(expected, resources)
+        expected_querystring = (
+            'resources=DISK_GB%3A15%2CMEMORY_MB%3A1024%2CVCPU%3A1'
+        )
+        self.assertEqual(expected_querystring, resources.to_querystring())
+
     @mock.patch('nova.compute.utils.is_volume_backed_instance',
                 return_value=False)
     def test_resources_from_flavor_no_bfv(self, mock_is_bfv):