[OVN] Tune OVN routers to reduce the mem footprint for ML2/OVN

In order to avoid having a MAC_Binding table explosion and helping
lowering the memory footprint when using ML2/OVN this patch is setting
two options to the OVN routers:

* always_learn_from_arp_request: By setting this to False we
  avoid learning from ARP replies observed in the network. Only the
  ARP requests sent by OVN will generate a MAC_Binding entry in the
  OVSDB database. For larger broadcasts domains this avoids having a
  MAC_Binding table explosion, reduce the DB size and memory footprint
  of ML2/OVN.

* dynamic_neigh_routers: By setting this to True we avoid
  pre-populating flows for router to router communication, reduding
  the number of flows, DB size and memory footprint of ML2/OVN.

For more information on these option for core OVN please refer to:
https://www.ovn.org/support/dist-docs/ovn-nb.5.html

This patch also includes a new maintenance task to include these options
to existing routers in the system.

Related-Bug: #1946318
Change-Id: I056acdec9b6ee2341d2bc4f7bd9a678f3bf91972
Signed-off-by: Lucas Alvares Gomes <lucasagomes@gmail.com>
(cherry picked from commit a278c5ba78)

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

@@ -14,6 +14,7 @@
 #    under the License.
 
 import abc
+import copy
 import inspect
 import threading
 
@@ -675,6 +676,31 @@ class DBInconsistenciesPeriodics(SchemaAwarePeriodicsBase):
 
         raise periodics.NeverAgain()
 
+    # TODO(lucasagomes): Remove this in the Z cycle
+    # A static spacing value is used here, but this method will only run
+    # once per lock due to the use of periodics.NeverAgain().
+    @periodics.periodic(spacing=600, run_immediately=True)
+    def check_router_mac_binding_options(self):
+        if not self.has_lock:
+            return
+
+        cmds = []
+        for router in self._nb_idl.lr_list().execute(check_error=True):
+            if (router.options.get('always_learn_from_arp_request') and
+                    router.options.get('dynamic_neigh_routers')):
+                continue
+
+            opts = copy.deepcopy(router.options)
+            opts.update({'always_learn_from_arp_request': 'false',
+                         'dynamic_neigh_routers': 'true'})
+            cmds.append(self._nb_idl.update_lrouter(router.name, options=opts))
+
+        if cmds:
+            with self._nb_idl.transaction(check_error=True) as txn:
+                for cmd in cmds:
+                    txn.add(cmd)
+        raise periodics.NeverAgain()
+
 
 class HashRingHealthCheckPeriodics(object):
 

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

@@ -1170,11 +1170,13 @@ class OVNClient(object):
         enabled = router.get('admin_state_up')
         lrouter_name = utils.ovn_name(router['id'])
         added_gw_port = None
+        options = {'always_learn_from_arp_request': 'false',
+                   'dynamic_neigh_routers': 'true'}
         with self._nb_idl.transaction(check_error=True) as txn:
             txn.add(self._nb_idl.create_lrouter(lrouter_name,
                                                 external_ids=external_ids,
                                                 enabled=enabled,
-                                                options={}))
+                                                options=options))
             # TODO(lucasagomes): add_external_gateway is being only used
             # by the ovn_db_sync.py script, remove it after the database
             # synchronization work

neutron/tests/unit/plugins/ml2/drivers/ovn/mech_driver/ovsdb/test_maintenance.py

@@ -432,3 +432,31 @@ class TestDBInconsistenciesPeriodics(testlib_api.SqlTestCaseLight,
             mock.call('lsp5', mcast_flood_reports='true', mcast_flood='false')]
 
         nb_idl.lsp_set_options.assert_has_calls(expected_calls)
+
+    def test_check_router_mac_binding_options(self):
+        nb_idl = self.fake_ovn_client._nb_idl
+        lr0 = fakes.FakeOvsdbRow.create_one_ovsdb_row(
+            attrs={'name': 'lr0',
+                   'options': {'always_learn_from_arp_request': 'false',
+                               'dynamic_neigh_routers': 'true'}})
+        lr1 = fakes.FakeOvsdbRow.create_one_ovsdb_row(
+            attrs={'name': 'lr1', 'options': {}})
+        lr2 = fakes.FakeOvsdbRow.create_one_ovsdb_row(
+            attrs={'name': 'lr2', 'options': {}})
+        nb_idl.lr_list.return_value.execute.return_value = [lr0, lr1, lr2]
+
+        # Invoke the periodic method, it meant to run only once at startup
+        # so NeverAgain will be raised at the end
+        self.assertRaises(periodics.NeverAgain,
+                          self.periodic.check_router_mac_binding_options)
+
+        # Assert lr1 and lr2 had their options updated since the values
+        # were not set
+        expected_calls = [
+            mock.call('lr1',
+                      options={'always_learn_from_arp_request': 'false',
+                               'dynamic_neigh_routers': 'true'}),
+            mock.call('lr2',
+                      options={'always_learn_from_arp_request': 'false',
+                               'dynamic_neigh_routers': 'true'})]
+        nb_idl.update_lrouter.assert_has_calls(expected_calls)

neutron/tests/unit/services/ovn_l3/test_plugin.py

@@ -538,7 +538,8 @@ class TestOVNL3RouterPlugin(test_mech_driver.Ml2PluginV2TestCase):
                         ovn_const.OVN_ROUTER_AZ_HINTS_EXT_ID_KEY: ''}
         self.l3_inst._ovn.create_lrouter.assert_called_once_with(
             'neutron-router-id', external_ids=external_ids,
-            enabled=True, options={})
+            enabled=True, options={'always_learn_from_arp_request': 'false',
+                                   'dynamic_neigh_routers': 'true'})
         self.l3_inst._ovn.add_lrouter_port.assert_called_once_with(
             **self.fake_ext_gw_port_assert)
         expected_calls = [