Sync CDM among Decision Engines by using notification pool

This commit allows to consume notifications via notifications pools[1].
Listeners in notification pools recieves a copy of notification. It
will let Watcher to sync Data Models of Decision Engines.

[1]: https://docs.openstack.org/oslo.messaging/ocata/notification_listener.html

Change-Id: Ie37528263181924f84510500fc1277b0237c1df8
Partially-Implements: blueprint support-watcher-ha-active-active-mode

.zuul.yaml

@@ -73,7 +73,7 @@
                 live_migration_uri: 'qemu+ssh://root@%s/system'
         devstack_services:
           watcher-api: false
-          watcher-decision-engine: false
+          watcher-decision-engine: true
           watcher-applier: false
           # We need to add TLS support for watcher plugin
           tls-proxy: false

watcher/common/service.py

@@ -251,11 +251,18 @@ class Service(service.ServiceBase):
 
     def build_notification_handler(self, topic_names, endpoints=()):
         serializer = rpc.RequestContextSerializer(rpc.JsonPayloadSerializer())
-        targets = [om.Target(topic=topic_name) for topic_name in topic_names]
+        targets = []
+        for topic in topic_names:
+            kwargs = {}
+            if '.' in topic:
+                exchange, topic = topic.split('.')
+                kwargs['exchange'] = exchange
+            kwargs['topic'] = topic
+            targets.append(om.Target(**kwargs))
         return om.get_notification_listener(
             self.notification_transport, targets, endpoints,
             executor='eventlet', serializer=serializer,
-            allow_requeue=False)
+            allow_requeue=False, pool=CONF.host)
 
     def start(self):
         LOG.debug("Connecting to '%s' (%s)",

watcher/conf/decision_engine.py

@@ -30,9 +30,12 @@ WATCHER_DECISION_ENGINE_OPTS = [
                     'control events, this topic '
                     'used for RPC calls'),
     cfg.ListOpt('notification_topics',
-                default=['versioned_notifications', 'watcher_notifications'],
-                help='The topic names from which notification events '
-                     'will be listened to'),
+                default=['nova.versioned_notifications',
+                         'watcher.watcher_notifications'],
+                help='The exchange and topic names from which '
+                     'notification events will be listened to. '
+                     'The exchange should be specified to get '
+                     'an ability to use pools.'),
     cfg.StrOpt('publisher_id',
                default='watcher.decision.api',
                help='The identifier used by the Watcher '