Unnecessary routers should not be created

We observe an excessive amount of routers created on
compute node on which some virtual machines got a fixed
ip on floating network.

Rpc servers should filter out those unnecessary routers
during syncing.

Conflicts:
    neutron/tests/unit/db/test_agentschedulers_db.py

Change-Id: I299031a505f05cd0469e2476b867b9dbca59c5bf
Partial-Bug: #1840579
(cherry picked from commit 480b04ce04)

neutron/db/l3_dvrscheduler_db.py

@@ -166,12 +166,18 @@ class L3_DVRsch_db_mixin(l3agent_sch_db.L3AgentSchedulerDbMixin):
             router_ids.add(subnet_port['device_id'])
         return router_ids
 
-    def get_subnet_ids_on_router(self, context, router_id):
+    def get_subnet_ids_on_router(self, context, router_id,
+                                 keep_gateway_port=True):
         """Return subnet IDs for interfaces attached to the given router."""
         subnet_ids = set()
         filter_rtr = {'device_id': [router_id]}
         int_ports = self._core_plugin.get_ports(context, filters=filter_rtr)
+
         for int_port in int_ports:
+            if (not keep_gateway_port and
+                    int_port['device_owner'] ==
+                    n_const.DEVICE_OWNER_ROUTER_GW):
+                continue
             int_ips = int_port['fixed_ips']
             if int_ips:
                 int_subnet = int_ips[0]['subnet_id']
@@ -421,7 +427,7 @@ class L3_DVRsch_db_mixin(l3agent_sch_db.L3AgentSchedulerDbMixin):
             else:
                 for router_id in (router_ids - result_set):
                     subnet_ids = self.get_subnet_ids_on_router(
-                        context, router_id)
+                        context, router_id, keep_gateway_port=False)
                     if (subnet_ids and
                             self._check_dvr_serviceable_ports_on_host(
                                     context, agent_db['host'],

neutron/tests/unit/db/test_agentschedulers_db.py

@@ -16,6 +16,7 @@
 import datetime
 
 import mock
+from neutron_lib.api.definitions import portbindings
 from neutron_lib import constants
 from neutron_lib import context
 from neutron_lib.plugins import constants as plugin_constants
@@ -1001,6 +1002,44 @@ class OvsAgentSchedulerTestCase(OvsAgentSchedulerTestCaseBase):
                 # No router will be auto scheduled.
                 self.assertEqual(0, len(host_routers['routers']))
 
+    def test_sync_dvr_router_with_fixedip_on_fip_net(self):
+        l3_rpc_cb = l3_rpc.L3RpcCallback()
+        self._register_dvr_agents()
+
+        with self.subnet() as s:
+            # first create an external network
+            net_id = s['subnet']['network_id']
+            self._set_net_external(net_id)
+            # create router with external gateway
+            router_data = {'name': 'router1',
+                           'external_gateway_info': {'network_id': net_id},
+                           'tenant_id': 'tenant_id',
+                           'admin_state_up': True,
+                           'distributed': True}
+            router = self.l3plugin.create_router(self.adminContext,
+                                                 {'router': router_data})
+            self.l3plugin.schedule_router(self.adminContext, router['id'])
+            with self.port(subnet=s,
+                           device_owner=DEVICE_OWNER_COMPUTE) as port:
+                # bind port to L3_HOSTB
+                updated_port = {
+                    "port": {
+                        portbindings.HOST_ID: L3_HOSTB
+                    }
+                }
+                self.plugin.update_port(
+                    self.adminContext,
+                    port['port']['id'],
+                    updated_port
+                )
+                ret_b = l3_rpc_cb.sync_routers(
+                    self.adminContext,
+                    host=L3_HOSTB,
+                    router_ids=[router['id']])
+
+                router_ids = [r['id'] for r in ret_b]
+                self.assertEqual(0, len(router_ids))
+
     def test_router_without_l3_agents(self):
         with self.subnet() as s:
             self._set_net_external(s['subnet']['network_id'])