Ensure traffic is not centralized if DVR is enabled

There is no need to clear the external_mac if DVR is enabled, not
even when the port is down. This patch ensures the external_mac is
only deleted when DVR is not enabled.

Without this patch, if a VM with a floating IP gets deleted, and
DVR is enabled, during some time the traffic gets (wrongly)
centralized while it should not. And it is also generating more
load on the OVN side unnecesarily.

Closes-Bug: #2025264

Change-Id: I89db15dd1b629bc963f3b63926391a4a02cbedf7
(cherry picked from commit 0090572b93)

neutron/plugins/ml2/drivers/ovn/mech_driver/mech_driver.py

@@ -1048,7 +1048,7 @@ class OVNMechanismDriver(api.MechanismDriver):
         # See doc/source/design/ovn_worker.rst for more details.
         return [worker.MaintenanceWorker()]
 
-    def _update_dnat_entry_if_needed(self, port_id, up=True):
+    def _update_dnat_entry_if_needed(self, port_id):
         """Update DNAT entry if using distributed floating ips."""
         if not self.nb_ovn:
             self.nb_ovn = self._ovn_client._nb_idl
@@ -1069,9 +1069,9 @@ class OVNMechanismDriver(api.MechanismDriver):
                                {ovn_const.OVN_FIP_EXT_MAC_KEY:
                                 nat['external_mac']})).execute()
 
-        if up and ovn_conf.is_ovn_distributed_floating_ip():
-            mac = nat['external_ids'][ovn_const.OVN_FIP_EXT_MAC_KEY]
-            if nat['external_mac'] != mac:
+        if ovn_conf.is_ovn_distributed_floating_ip():
+            mac = nat['external_ids'].get(ovn_const.OVN_FIP_EXT_MAC_KEY)
+            if mac and nat['external_mac'] != mac:
                 LOG.debug("Setting external_mac of port %s to %s",
                           port_id, mac)
                 self.nb_ovn.db_set(
@@ -1137,7 +1137,7 @@ class OVNMechanismDriver(api.MechanismDriver):
         # to prevent another entity from bypassing the block with its own
         # port status update.
         LOG.info("OVN reports status down for port: %s", port_id)
-        self._update_dnat_entry_if_needed(port_id, False)
+        self._update_dnat_entry_if_needed(port_id)
         admin_context = n_context.get_admin_context()
         try:
             db_port = ml2_db.get_port(admin_context, port_id)

neutron/tests/unit/plugins/ml2/drivers/ovn/mech_driver/test_mech_driver.py

@@ -1124,7 +1124,7 @@ class TestOVNMechanismDriver(TestOVNMechanismDriverBase):
                 resources.PORT,
                 provisioning_blocks.L2_AGENT_ENTITY
             )
-            ude.assert_called_once_with(port1['port']['id'], False)
+            ude.assert_called_once_with(port1['port']['id'])
 
             # If the port does NOT bellong to compute, do not notify Nova
             # about it's status changes
@@ -1174,7 +1174,7 @@ class TestOVNMechanismDriver(TestOVNMechanismDriverBase):
                 resources.PORT,
                 provisioning_blocks.L2_AGENT_ENTITY
             )
-            ude.assert_called_once_with(port1['port']['id'], False)
+            ude.assert_called_once_with(port1['port']['id'])
 
     def test_bind_port_unsupported_vnic_type(self):
         fake_port = fakes.FakePort.create_one_port(
@@ -2368,9 +2368,10 @@ class TestOVNMechanismDriver(TestOVNMechanismDriverBase):
         self.assertTrue(agent.alive, "Agent of type %s alive=%s" % (
             agent.agent_type, agent.alive))
 
-    def _test__update_dnat_entry_if_needed(self, up=True):
-        ovn_conf.cfg.CONF.set_override(
-            'enable_distributed_floating_ip', True, group='ovn')
+    def _test__update_dnat_entry_if_needed(self, dvr=True):
+        if dvr:
+            ovn_conf.cfg.CONF.set_override(
+                'enable_distributed_floating_ip', True, group='ovn')
         port_id = 'fake-port-id'
         fake_ext_mac_key = 'fake-ext-mac-key'
         fake_nat_uuid = uuidutils.generate_uuid()
@@ -2383,22 +2384,24 @@ class TestOVNMechanismDriver(TestOVNMechanismDriverBase):
         fake_db_find.execute.return_value = [nat_row]
         self.nb_ovn.db_find.return_value = fake_db_find
 
-        self.mech_driver._update_dnat_entry_if_needed(port_id, up=up)
+        self.mech_driver._update_dnat_entry_if_needed(port_id)
 
-        if up:
+        if dvr:
             # Assert that we are setting the external_mac in the NAT table
             self.nb_ovn.db_set.assert_called_once_with(
                 'NAT', fake_nat_uuid, ('external_mac', fake_ext_mac_key))
+            self.nb_ovn.db_clear.assert_not_called()
         else:
+            self.nb_ovn.db_set.assert_not_called()
             # Assert that we are cleaning the external_mac from the NAT table
             self.nb_ovn.db_clear.assert_called_once_with(
                 'NAT', fake_nat_uuid, 'external_mac')
 
-    def test__update_dnat_entry_if_needed_up(self):
+    def test__update_dnat_entry_if_needed_dvr(self):
         self._test__update_dnat_entry_if_needed()
 
-    def test__update_dnat_entry_if_needed_down(self):
-        self._test__update_dnat_entry_if_needed(up=False)
+    def test__update_dnat_entry_if_needed_no_dvr(self):
+        self._test__update_dnat_entry_if_needed(dvr=False)
 
     @mock.patch('neutron.plugins.ml2.drivers.ovn.mech_driver.ovsdb.'
                 'ovn_client.OVNClient._get_router_ports')

releasenotes/notes/dvr-external-mac-934409413e515eb2.yaml

@@ -0,0 +1,10 @@
+---
+other:
+  - |
+    The external_mac entry in the NAT table is used to distribute/centralize
+    the traffic to the FIPs. When there is an external_mac set the traffic
+    is distributed (DVR). When it is empty it is centralized through the
+    gateway port (no DVR). Upon port status transition to down, the
+    external_mac was removed regardless of DVR being enabled or not, leading
+    to centralize the FIP traffic for DVR -- though it was for down ports that
+    won't accept traffic anyway.