[HA] Do not add initial state change delay in HA router

The initial state ("primary", "backup") should be set immediately.
in [1], a transition delay to "primary" was introduced. This delay
is unnecesary when the first state happens.

Closes-Bug: #1945512

[1]https://review.opendev.org/q/I70037da9cdd0f8448e0af8dd96b4e3f5de5728ad

Change-Id: Ibe9178c4126977f1321e414676d67f28e5ec9b57

neutron/agent/l3/ha.py

@@ -17,6 +17,9 @@ import os
 import threading
 
 import eventlet
+from neutron_lib.callbacks import events
+from neutron_lib.callbacks import registry
+from neutron_lib.callbacks import resources
 from neutron_lib import constants
 from oslo_log import log as logging
 from oslo_utils import fileutils
@@ -76,6 +79,7 @@ class L3AgentKeepalivedStateChangeServer(object):
         server.wait()
 
 
+@registry.has_registry_receivers
 class AgentMixin(object):
     def __init__(self, host):
         self._init_ha_conf_path()
@@ -87,6 +91,13 @@ class AgentMixin(object):
         eventlet.spawn(self._start_keepalived_notifications_server)
         self._transition_states = {}
         self._transition_state_mutex = threading.Lock()
+        self._initial_state_change_per_router = set()
+
+    def initial_state_change(self, router_id):
+        initial_state = router_id not in self._initial_state_change_per_router
+        if initial_state:
+            self._initial_state_change_per_router.add(router_id)
+        return initial_state
 
     def _get_router_info(self, router_id):
         try:
@@ -95,6 +106,13 @@ class AgentMixin(object):
             LOG.info('Router %s is not managed by this agent. It was '
                      'possibly deleted concurrently.', router_id)
 
+    @registry.receives(resources.ROUTER, [events.AFTER_DELETE])
+    def _delete_router(self, resource, event, trigger, payload):
+        try:
+            self._initial_state_change_per_router.remove(payload.resource_id)
+        except KeyError:
+            pass
+
     def check_ha_state_for_router(self, router_id, current_state):
         ri = self._get_router_info(router_id)
         if not ri:
@@ -148,7 +166,7 @@ class AgentMixin(object):
 
     def _enqueue_state_change(self, router_id, state):
         # NOTE(ralonsoh): move 'primary' and 'backup' constants to n-lib
-        if state == 'primary':
+        if state == 'primary' and not self.initial_state_change(router_id):
             eventlet.sleep(self.conf.ha_vrrp_advert_int)
         transition_state = self._update_transition_state(router_id)
         if transition_state != state:

neutron/tests/unit/agent/l3/test_agent.py

@@ -263,7 +263,15 @@ class TestBasicRouterOperations(BasicRouterOperationsFramework):
         self._enqueue_state_change_transitions(['backup'], 1)
 
     def test_enqueue_state_change_from_none_to_primary_to_backup(self):
-        self._enqueue_state_change_transitions(['primary', 'backup'], 0)
+        # First transition (to primary), won't have a delay.
+        self._enqueue_state_change_transitions(['primary', 'backup'], 2)
+
+    def test_enqueue_state_change_from_none_to_primary_to_backup_twice(self):
+        # Second transition to primary will have a delay and will be overridden
+        # by the second transition to backup; that means the transition from
+        # backup (second state) to primary (third state) is dismissed.
+        self._enqueue_state_change_transitions(
+            ['primary', 'backup', 'primary', 'backup'], 2)
 
     def test_enqueue_state_change_from_none_to_backup_to_primary(self):
         self._enqueue_state_change_transitions(['backup', 'primary'], 2)
@@ -2563,6 +2571,21 @@ class TestBasicRouterOperations(BasicRouterOperationsFramework):
         agent.router_removed_from_agent(None, {'router_id': FAKE_ID})
         self.assertEqual(1, agent._queue.add.call_count)
 
+    @mock.patch.object(metadata_driver.MetadataDriver,
+                       'destroy_monitored_metadata_proxy')
+    def test__router_removed(self, *args):
+        agent = l3_agent.L3NATAgent(HOSTNAME, self.conf)
+        ri = mock.Mock(router={'id': 'router_id'})
+        agent._initial_state_change_per_router.add('router_id')
+        self.assertEqual({'router_id'}, agent._initial_state_change_per_router)
+        for _ in range(2):
+            # The second call will trigger a KeyError exception in
+            # AgentMixin._delete_router that should be dismissed.
+            agent.router_info['router_id'] = mock.ANY
+            agent.pd = mock.Mock(routers={'router_id': {'subnets': []}})
+            agent._router_removed(ri, 'router_id')
+            self.assertEqual(set([]), agent._initial_state_change_per_router)
+
     def test_added_to_agent(self):
         agent = l3_agent.L3NATAgent(HOSTNAME, self.conf)
         agent._queue = mock.Mock()