[L3HA] Don't update HA router's ports if router isn't active on agents

In case when HA router isn't active on any L3 agent,
_ensure_host_set_on_port method shouldn't try to update port's host to
the host from which there was an rpc message sent, as this can be host
on which router is in the "standby" mode.
This method should only update port's host to the router's "active_host"
if there is such active_host found already.

Depends-On: https://review.opendev.org/c/openstack/requirements/+/841489

Closes-Bug: #1973162
Closes-Bug: #1942190
Change-Id: Ib3945d294601b35f9b268c25841cd284b52c4ca3

neutron/api/rpc/handlers/l3_rpc.py

@@ -224,22 +224,21 @@ class L3RpcCallback(object):
                     active_host = (
                         self.l3plugin.get_active_host_for_ha_router(
                             context, router_id))
-                    if active_host:
-                        host = active_host
-                    # If there is currently no active router instance (For
-                    # example it's a new router), the host that requested
-                    # the routers (Essentially a random host) will do. The
-                    # port binding will be corrected when an active is
-                    # elected.
+                    if not active_host:
+                        LOG.debug("Router %(router)s is not active on any "
+                                  "host. Port %(port)s will not be updated "
+                                  "now.",
+                                  {'router': router_id, 'port': port['id']})
+                        return
                     try:
                         LOG.debug("Updating router %(router)s port %(port)s "
                                   "binding host %(host)s",
                                   {"router": router_id, "port": port['id'],
-                                   "host": host})
+                                   "host": active_host})
                         self.plugin.update_port(
                             context,
                             port['id'],
-                            {'port': {portbindings.HOST_ID: host}})
+                            {'port': {portbindings.HOST_ID: active_host}})
                     except exceptions.PortNotFound:
                         LOG.debug("Port %(port)s not found while updating "
                                   "agent binding for router %(router)s.",

neutron/tests/unit/db/test_l3_hamode_db.py

@@ -1246,9 +1246,19 @@ class L3HAModeDbTestCase(L3HATestFramework):
             self.plugin.list_active_sync_routers_on_active_l3_agent(
                 self.admin_ctx, self.agent1['host'], [router['id']]))[0]
 
-        # ensure_host_set_on_ports binds an unbound port
         callback = l3_rpc.L3RpcCallback()
         callback._l3plugin = self.plugin
+        # First ensure that port is not bound if router is not active on any
+        # agent
+        callback._ensure_host_set_on_ports(
+            self.admin_ctx, self.agent1['host'], [router])
+        port = self._get_first_interface(router['id'])
+        self.assertEqual('', port[portbindings.HOST_ID])
+
+        # Now update router to be active on agent1
+        # and ensure_host_set_on_ports binds an unbound port
+        self.plugin.update_routers_states(
+            self.admin_ctx, {router['id']: 'active'}, self.agent1['host'])
         callback._ensure_host_set_on_ports(
             self.admin_ctx, self.agent1['host'], [router])
         port = self._get_first_interface(router['id'])