Schedule networks to new segments if needed

In case when subnet in segment X was created before hosts from
that segment was mapped in the Neutron DB, network wasn't scheduled
to the DHCP agents in that new segment.
Now DHCP scheduler is triggered in such case.

Closes-bug: #1917811
Change-Id: Ic9e64aa4ecdc3d56f00c26204ad931b810db7599

neutron/db/agentschedulers_db.py

@@ -17,12 +17,16 @@ import datetime
 import random
 import time
 
+from neutron_lib.callbacks import events
+from neutron_lib.callbacks import registry
+from neutron_lib.callbacks import resources
 from neutron_lib import constants
 from neutron_lib import context as ncontext
 from neutron_lib.db import api as db_api
 from neutron_lib import exceptions as n_exc
 from neutron_lib.exceptions import agent as agent_exc
 from neutron_lib.exceptions import dhcpagentscheduler as das_exc
+from neutron_lib.plugins import directory
 from oslo_config import cfg
 from oslo_log import log as logging
 import oslo_messaging
@@ -36,6 +40,7 @@ from neutron.db import agents_db
 from neutron.db.availability_zone import network as network_az
 from neutron.extensions import dhcpagentscheduler
 from neutron.objects import network
+from neutron.objects import subnet as subnet_obj
 from neutron import worker as neutron_worker
 
 
@@ -226,12 +231,15 @@ class DhcpAgentSchedulerDbMixin(dhcpagentscheduler
                              additional_time)
         return agent_expected_up > timeutils.utcnow()
 
-    def _schedule_network(self, context, network_id, dhcp_notifier):
+    def _schedule_network(self, context, network_id, dhcp_notifier,
+                          candidate_hosts=None):
         LOG.info("Scheduling unhosted network %s", network_id)
         try:
             # TODO(enikanorov): have to issue redundant db query
             # to satisfy scheduling interface
             network = self.get_network(context, network_id)
+            if candidate_hosts:
+                network['candidate_hosts'] = candidate_hosts
             agents = self.schedule_network(context, network)
             if not agents:
                 LOG.info("Failed to schedule network %s, "
@@ -481,6 +489,25 @@ class DhcpAgentSchedulerDbMixin(dhcpagentscheduler
         if self.network_scheduler:
             self.network_scheduler.auto_schedule_networks(self, context, host)
 
+    @registry.receives(resources.SEGMENT_HOST_MAPPING, [events.AFTER_CREATE])
+    def auto_schedule_new_network_segments(self, resource, event, trigger,
+                                           payload=None):
+        if not cfg.CONF.network_auto_schedule:
+            return
+        segment_plugin = directory.get_plugin('segments')
+        dhcp_notifier = self.agent_notifiers.get(constants.AGENT_TYPE_DHCP)
+        segment_ids = payload.metadata.get('current_segment_ids')
+        segments = segment_plugin.get_segments(
+            payload.context, filters={'id': segment_ids})
+        subnets = subnet_obj.Subnet.get_objects(
+            payload.context, segment_id=segment_ids)
+        network_ids = {s.network_id for s in subnets}
+        for network_id in network_ids:
+            for segment in segments:
+                self._schedule_network(
+                    payload.context, network_id, dhcp_notifier,
+                    candidate_hosts=segment['hosts'])
+
 
 class AZDhcpAgentSchedulerDbMixin(DhcpAgentSchedulerDbMixin,
                                   network_az.NetworkAvailabilityZoneMixin):

neutron/tests/unit/db/test_agentschedulers_db.py

@@ -18,6 +18,8 @@ from unittest import mock
 
 from neutron_lib.api.definitions import dhcpagentscheduler as das_apidef
 from neutron_lib.api.definitions import portbindings
+from neutron_lib.callbacks import events
+from neutron_lib.callbacks import resources
 from neutron_lib import constants
 from neutron_lib import context
 from neutron_lib.db import api as db_api
@@ -1588,6 +1590,47 @@ class OvsDhcpAgentNotifierTestCase(test_agent.AgentDBTestMixIn,
             for expected in low_expecteds:
                 self.assertIn(expected, self.dhcp_notifier_cast.call_args_list)
 
+    def _test_auto_schedule_new_network_segments(self, subnet_on_segment):
+        ctx = mock.Mock()
+        payload = events.DBEventPayload(
+            ctx,
+            metadata={'host': 'HOST A',
+                      'current_segment_ids': set(['segment-1'])})
+        segments_plugin = mock.Mock()
+        segments_plugin.get_segments.return_value = [
+            {'id': 'segment-1', 'hosts': ['HOST A']}]
+        dhcp_notifier = mock.Mock()
+        dhcp_mixin = agentschedulers_db.DhcpAgentSchedulerDbMixin()
+        with mock.patch(
+                'neutron_lib.plugins.directory.get_plugin',
+                return_value=segments_plugin), \
+            mock.patch(
+                'neutron.objects.subnet.Subnet.get_objects') as get_subnets, \
+            mock.patch.object(
+                dhcp_mixin, '_schedule_network') as schedule_network:
+
+            get_subnets.return_value = (
+                [subnet_on_segment] if subnet_on_segment else [])
+
+            dhcp_mixin.agent_notifiers[constants.AGENT_TYPE_DHCP] = (
+                dhcp_notifier)
+            dhcp_mixin.auto_schedule_new_network_segments(
+                resources.SEGMENT_HOST_MAPPING, events.AFTER_CREATE,
+                ctx, payload)
+            if subnet_on_segment:
+                schedule_network.assert_called_once_with(
+                    ctx, subnet_on_segment.network_id,
+                    dhcp_notifier, candidate_hosts=['HOST A'])
+            else:
+                schedule_network.assert_not_called()
+
+    def test_auto_schedule_new_network_segments(self):
+        self._test_auto_schedule_new_network_segments(
+            subnet_on_segment=mock.Mock(network_id='net-1'))
+
+    def test_auto_schedule_new_network_segments_no_networks_on_segment(self):
+        self._test_auto_schedule_new_network_segments(subnet_on_segment=None)
+
     def _is_schedule_network_called(self, device_id):
         dhcp_notifier_schedule = mock.patch(
             'neutron.api.rpc.agentnotifiers.dhcp_rpc_agent_api.'