gnocchi: always set needed_overlap for aggregation

gnocchi_aggregation_by_resources_threshold set needed_overlap
to workaround #1479429, we should do the same for
gnocchi_aggregation_by_metrics_threshold.

This change does it.

Related-bug: #1479429
Change-Id: I283200e23d69dbd174f990722711d6b538fe42e3

aodh/evaluator/gnocchi.py

@@ -70,10 +70,19 @@ class GnocchiResourceThresholdEvaluator(GnocchiBase):
 class GnocchiAggregationMetricsThresholdEvaluator(GnocchiBase):
     def _statistics(self, rule, start, end):
         try:
+            # FIXME(sileht): In case of a heat autoscaling stack decide to
+            # delete an instance, the gnocchi metrics associated to this
+            # instance will be no more updated and when the alarm will ask
+            # for the aggregation, gnocchi will raise a 'No overlap'
+            # exception.
+            # So temporary set 'needed_overlap' to 0 to disable the
+            # gnocchi checks about missing points. For more detail see:
+            #   https://bugs.launchpad.net/gnocchi/+bug/1479429
             return self._gnocchi_client.metric.aggregation(
                 metrics=rule['metrics'],
                 start=start, stop=end,
-                aggregation=rule['aggregation_method'])
+                aggregation=rule['aggregation_method'],
+                needed_overlap=0)
         except Exception as e:
             LOG.warning(_LW('alarm stats retrieval failed: %s'), e)
             return []

aodh/tests/unit/evaluator/test_gnocchi.py

@@ -326,6 +326,7 @@ class TestGnocchiAggregationMetricsThresholdEvaluate(TestGnocchiEvaluatorBase):
                                    metrics=[
                                        '0bb1604d-1193-4c0a-b4b8-74b170e35e83',
                                        '9ddc209f-42f8-41e1-b8f1-8804f59c4053'],
+                                   needed_overlap=0,
                                    start=start_alarm, stop=end)],
             self.client.metric.mock_calls)
         self._assert_all_alarms('alarm')