Clear DVR MAC on last agent deletion from host

Once all agents are deleted from a host, the DVR MAC generated
for that host should be deleted as well to prevent a buildup of
pointless flows generated in the OVS agent for hosts that don't
exist.

Closes-Bug: #1568206
Change-Id: I51e736aa0431980a595ecf810f148ca62d990d20

neutron/callbacks/resources.py

@@ -11,6 +11,7 @@
 #    under the License.
 
 # String literals representing core resources.
+AGENT = 'agent'
 EXTERNAL_NETWORK = 'external_network'
 FLOATING_IP = 'floating_ip'
 PORT = 'port'

neutron/db/agents_db.py

@@ -31,6 +31,9 @@ from sqlalchemy import sql
 from neutron._i18n import _, _LE, _LI, _LW
 from neutron.api.rpc.callbacks import version_manager
 from neutron.api.v2 import attributes
+from neutron.callbacks import events
+from neutron.callbacks import registry
+from neutron.callbacks import resources
 from neutron.common import constants
 from neutron import context
 from neutron.db import api as db_api
@@ -251,8 +254,10 @@ class AgentDbMixin(ext_agent.AgentPluginBase, AgentAvailabilityZoneMixin):
         return self._fields(res, fields)
 
     def delete_agent(self, context, id):
+        agent = self._get_agent(context, id)
+        registry.notify(resources.AGENT, events.BEFORE_DELETE, self,
+                        context=context, agent=agent)
         with context.session.begin(subtransactions=True):
-            agent = self._get_agent(context, id)
             context.session.delete(agent)
 
     def update_agent(self, context, id, agent):

neutron/db/dvr_mac_db.py

@@ -22,6 +22,9 @@ from sqlalchemy import or_
 from sqlalchemy.orm import exc
 
 from neutron._i18n import _, _LE
+from neutron.callbacks import events
+from neutron.callbacks import registry
+from neutron.callbacks import resources
 from neutron.common import constants
 from neutron.common import exceptions as n_exc
 from neutron.common import utils
@@ -60,9 +63,36 @@ class DistributedVirtualRouterMacAddress(model_base.BASEV2):
     mac_address = sa.Column(sa.String(32), nullable=False, unique=True)
 
 
+def _delete_mac_associated_with_agent(resource, event, trigger, context, agent,
+                                      **kwargs):
+    host = agent['host']
+    plugin = manager.NeutronManager.get_plugin()
+    if [a for a in plugin.get_agents(context, filters={'host': [host]})
+            if a['id'] != agent['id']]:
+        # there are still agents on this host, don't mess with the mac entry
+        # until they are all deleted.
+        return
+    try:
+        with context.session.begin(subtransactions=True):
+            entry = (context.session.query(DistributedVirtualRouterMacAddress).
+                     filter(DistributedVirtualRouterMacAddress.host == host).
+                     one())
+            context.session.delete(entry)
+    except exc.NoResultFound:
+        return
+    # notify remaining agents so they cleanup flows
+    dvr_macs = plugin.get_dvr_mac_address_list(context)
+    plugin.notifier.dvr_mac_address_update(context, dvr_macs)
+
+
 class DVRDbMixin(ext_dvr.DVRMacAddressPluginBase):
     """Mixin class to add dvr mac address to db_plugin_base_v2."""
 
+    def __new__(cls, *args, **kwargs):
+        registry.subscribe(_delete_mac_associated_with_agent,
+                           resources.AGENT, events.BEFORE_DELETE)
+        return super(DVRDbMixin, cls).__new__(cls)
+
     @property
     def plugin(self):
         try:

neutron/tests/unit/db/test_dvr_mac_db.py

@@ -16,11 +16,15 @@
 import mock
 from oslo_config import cfg
 
+from neutron.callbacks import events
+from neutron.callbacks import registry
+from neutron.callbacks import resources
 from neutron.common import constants
 from neutron import context
 from neutron.db import dvr_mac_db
 from neutron.extensions import dvr
 from neutron.extensions import portbindings
+from neutron import manager
 from neutron.tests.unit.plugins.ml2 import test_plugin
 
 
@@ -75,6 +79,34 @@ class DvrDbMixinTestCase(test_plugin.Ml2PluginV2TestCase):
                               self.ctx, "foo_host_2")
         self.assertEqual(new_retries, f.call_count)
 
+    def test_mac_not_cleared_on_agent_delete_event_with_remaining_agents(self):
+        plugin = manager.NeutronManager.get_plugin()
+        self._create_dvr_mac_entry('host_1', 'mac_1')
+        self._create_dvr_mac_entry('host_2', 'mac_2')
+        agent1 = {'host': 'host_1', 'id': 'a1'}
+        agent2 = {'host': 'host_1', 'id': 'a2'}
+        with mock.patch.object(plugin, 'get_agents', return_value=[agent2]):
+            with mock.patch.object(plugin, 'notifier') as notifier:
+                registry.notify(resources.AGENT, events.BEFORE_DELETE, self,
+                                context=self.ctx, agent=agent1)
+        mac_list = self.mixin.get_dvr_mac_address_list(self.ctx)
+        self.assertEqual(2, len(mac_list))
+        self.assertFalse(notifier.dvr_mac_address_update.called)
+
+    def test_mac_cleared_on_agent_delete_event(self):
+        plugin = manager.NeutronManager.get_plugin()
+        self._create_dvr_mac_entry('host_1', 'mac_1')
+        self._create_dvr_mac_entry('host_2', 'mac_2')
+        agent = {'host': 'host_1', 'id': 'a1'}
+        with mock.patch.object(plugin, 'notifier') as notifier:
+            registry.notify(resources.AGENT, events.BEFORE_DELETE, self,
+                            context=self.ctx, agent=agent)
+        mac_list = self.mixin.get_dvr_mac_address_list(self.ctx)
+        self.assertEqual(1, len(mac_list))
+        self.assertEqual('host_2', mac_list[0]['host'])
+        notifier.dvr_mac_address_update.assert_called_once_with(
+            self.ctx, mac_list)
+
     def test_get_dvr_mac_address_list(self):
         self._create_dvr_mac_entry('host_1', 'mac_1')
         self._create_dvr_mac_entry('host_2', 'mac_2')