DVR: Fix neutron metering agent to notify hosts hosting DVR

DVR router updates are notified based on where they are hosted.
But in the case of metering rpc notifier the notification to a
specific host was not implemented and also when a call is being
made to routers_updated_on_host, it is being ignored since it only
implements the routers_updated function call.

Change-Id: I39b0d43b14294a8eecf6cba230d948c2c45a0b7a
Closes-Bug: #1682345

neutron/api/rpc/agentnotifiers/metering_rpc_agent_api.py

@@ -70,6 +70,14 @@ class MeteringAgentNotifyAPI(object):
         cctxt = self.client.prepare(fanout=True)
         cctxt.cast(context, method, router_id=router_id)
 
+    def _notification_host(self, context, method, host, **kwargs):
+        """Notify the agent that is hosting the router."""
+        LOG.debug('Notify agent at %(host)s the message '
+                  '%(method)s', {'host': host,
+                                 'method': method})
+        cctxt = self.client.prepare(server=host)
+        cctxt.cast(context, method, **kwargs)
+
     def _notification(self, context, method, routers):
         """Notify all the agents that are hosting the routers."""
         plugin = directory.get_plugin(plugin_constants.L3)
@@ -101,3 +109,8 @@ class MeteringAgentNotifyAPI(object):
 
     def remove_metering_label(self, context, routers):
         self._notification(context, 'remove_metering_label', routers)
+
+    def routers_updated_on_host(self, context, router_ids, host):
+        """Notify router updates to specific hosts hosting DVR routers."""
+        self._notification_host(context, 'routers_updated', host,
+                                routers=router_ids)

neutron/tests/unit/services/metering/test_metering_plugin.py

@@ -17,6 +17,7 @@ from neutron_lib import context
 from neutron_lib.plugins import directory
 from oslo_utils import uuidutils
 
+from neutron.api.rpc.agentnotifiers import metering_rpc_agent_api
 from neutron.api.v2 import attributes as attr
 from neutron.common import utils
 from neutron.db import api as db_api
@@ -133,6 +134,23 @@ class TestMeteringPlugin(test_db_base_plugin_v2.NeutronDbPluginV2TestCase,
         self.remove_rule_patch = mock.patch(remove_rule)
         self.mock_remove_rule = self.remove_rule_patch.start()
 
+    def test_routers_updated_on_host_rpc_call(self):
+        router_test = {
+            'id': 'xyz',
+            'name': 'testrouter'}
+        notify_host = ('neutron.api.rpc.agentnotifiers.' +
+                       'metering_rpc_agent_api.MeteringAgentNotifyAPI' +
+                       '._notification_host')
+        self.notify_patch = mock.patch(notify_host)
+        self.mock_notify_host = self.notify_patch.start()
+        metering_rpc_handle = metering_rpc_agent_api.MeteringAgentNotifyAPI()
+        metering_rpc_handle.routers_updated_on_host(
+            self.ctx,
+            [router_test['id']],
+            'test_host')
+        self.mock_notify_host.assert_called_with(self.ctx, 'routers_updated',
+                                                 'test_host', routers=['xyz'])
+
     def test_add_metering_label_rpc_call(self):
         second_uuid = 'e27fe2df-376e-4ac7-ae13-92f050a21f84'
         expected = [{'status': 'ACTIVE',