gnocchi: percent_of_overlap=0 for agg. alarms

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 'percent_of_overlap' to 0 to disable the
gnocchi checks about missing points.

And adds some docs about the importance of filter out resource
with ended_at != 'null'.

For more detail see:
  https://bugs.launchpad.net/gnocchi/+bug/1479429

Related bug: #1479429

Change-Id: I528d21c048d84b9552febd08f787812c668983ab

aodh/api/controllers/v2/alarm_rules/gnocchi.py

@@ -123,7 +123,10 @@ class AggregationMetricByResourcesLookupRule(AlarmGnocchiThresholdRule):
     "The name of the metric"
 
     query = wsme.wsattr(wtypes.text, mandatory=True)
-    "The query to filter the metric"
+    ('The query to filter the metric, Don\'t forget to filter out '
+     'deleted resources (example: {"and": [{"=": {"ended_at": null}}, ...]}), '
+     'Otherwise Gnocchi will try to create the aggregate against obsolete '
+     'resources')
 
     resource_type = wsme.wsattr(wtypes.text, mandatory=True)
     "The resource type"

aodh/evaluator/gnocchi.py

@@ -60,6 +60,14 @@ class GnocchiThresholdEvaluator(threshold.ThresholdEvaluator):
             req['url'] += "/aggregation/resource/%s/metric/%s" % (
                 alarm.rule['resource_type'], alarm.rule['metric'])
             req['data'] = alarm.rule['query']
+            # 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 'percent_of_overlap' to 0 to disable the
+            # gnocchi checks about missing points. For more detail see:
+            #   https://bugs.launchpad.net/gnocchi/+bug/1479429
+            req['params']['percent_of_overlap'] = 0
 
         elif alarm.type == 'gnocchi_aggregation_by_metrics_threshold':
             req['url'] += "/aggregation/metric"

aodh/tests/evaluator/test_gnocchi.py

@@ -227,7 +227,8 @@ class TestGnocchiThresholdEvaluate(base.TestEvaluatorBase):
             mock.call(url='http://localhost:8041/v1/aggregation/resource/'
                       'instance/metric/cpu_util',
                       params={'aggregation': 'mean',
-                              'start': start_alarm3, 'end': end},
+                              'start': start_alarm3, 'end': end,
+                              'percent_of_overlap': 0},
                       data='{"=": {"server_group": "my_autoscaling_group"}}',
                       headers=expected_headers),
             ],