Use write connection for get_vpn_services_on_host

The OVN IPSEC implementation requires write connection.
And it will raise errors when try to bind routers with
`Can't upgrade a READER transaction to a WRITER mid-transaction`.

This alias both to write transation declear so no above error will
raise.

Closes-Bug: 2100911
Change-Id: I1f5ddbaae7b9a45382ee1307c13f26d346b03644

neutron_vpnaas/services/vpn/service_drivers/base_ipsec.py

@@ -71,7 +71,7 @@ class IPsecVpnDriverCallBack:
             self.driver.name)
         return query
 
-    @db_api.CONTEXT_READER
+    @db_api.CONTEXT_WRITER
     def get_vpn_services_on_host(self, context, host=None):
         """Returns the vpnservices on the host."""
         vpnservices = self._get_agent_hosting_vpn_services(

neutron_vpnaas/tests/unit/db/vpn/test_vpn_agentschedulers_db.py

@@ -24,6 +24,7 @@ from neutron.tests.unit.api import test_extensions
 from neutron.tests.unit.extensions import test_l3
 from neutron.tests.unit import testlib_api
 from neutron_lib import context
+from neutron_lib.db import api as db_api
 from neutron_lib import exceptions as n_exc
 from neutron_lib.plugins import constants as plugin_constants
 from neutron_lib.plugins import directory
@@ -330,6 +331,46 @@ class VPNAgentSchedulerTestCase(VPNAgentSchedulerTestCaseBase):
         self.assertEqual(VPN_HOSTA, host_before)
         self.assertEqual(VPN_HOSTB, host_after)
 
+    def test_router_reschedule_with_write_db_wrap(self):
+        self._register_agent_states()
+        agent_a = self.service_plugin.get_vpn_agent_on_host(
+            self.adminContext, VPN_HOSTA)
+
+        with self.vpnservice() as service:
+            # schedule the vpn routers to agent A
+            with db_api.CONTEXT_WRITER.using(self.adminContext):
+                self.service_plugin.auto_schedule_routers(
+                    self.adminContext, agent_a)
+            ctxt_mock = mock.MagicMock()
+            call_mock = mock.MagicMock(
+                side_effect=[oslo_messaging.MessagingTimeout, None])
+            ctxt_mock.call = call_mock
+            self.client_mock.prepare = mock.MagicMock(return_value=ctxt_mock)
+            self._take_down_agent_and_run_reschedule(VPN_HOSTA)
+            self.assertEqual(2, call_mock.call_count)
+            # make sure vpn service was rescheduled even when first attempt
+            # failed to notify VPN agent
+            router_id = service['vpnservice']['router_id']
+            host = self._get_agent_host_by_router(router_id)
+
+            vpn_agents = self._list_vpn_agents_hosting_router(router_id)
+            self.assertEqual(1, len(vpn_agents['agents']))
+            self.assertEqual(VPN_HOSTB, host)
+
+    def test_router_reschedule_with_read_db_wrap(self):
+        self._register_agent_states()
+        agent_a = self.service_plugin.get_vpn_agent_on_host(
+            self.adminContext, VPN_HOSTA)
+
+        with self.vpnservice():
+            # schedule the vpn routers to agent A
+            with db_api.CONTEXT_READER.using(self.adminContext):
+                self.assertRaises(
+                    TypeError,
+                    self.service_plugin.auto_schedule_routers,
+                    self.adminContext,
+                    agent_a)
+
     def test_router_reschedule_succeeded_after_failed_notification(self):
         self._register_agent_states()
         agent_a = self.service_plugin.get_vpn_agent_on_host(

neutron_vpnaas/tests/unit/services/vpn/service_drivers/test_ovn_ipsec.py

@@ -130,9 +130,12 @@ class TestOvnIPsecDriver(base.BaseTestCase):
             router_id=FAKE_ROUTER_ID,
             router=self._fake_router
         )
+        self.svc_plugin.get_vpn_agent_on_host.return_value = {'id': FAKE_HOST}
         self.svc_plugin.get_vpnservice.return_value = FAKE_VPNSERVICE_1
         self.svc_plugin.get_vpnservice_router_id.return_value = FAKE_ROUTER_ID
         self.driver = ipsec_driver.IPsecOvnVPNDriver(self.svc_plugin)
+        self.driver.make_vpnservice_dict = mock.Mock(
+            return_value={'id': FAKE_HOST})
         self.validator = ipsec_validator.IpsecVpnValidator(self.driver)
         self.context = n_ctx.get_admin_context()
 
@@ -304,3 +307,51 @@ class TestOvnIPsecDriver(base.BaseTestCase):
             [FAKE_VPN_CONNECTION_1],
             expected_add, expected_remove
         )
+
+
+class TestOvnIPsecCallBackDriver(base.BaseTestCase):
+    def setUp(self):
+        super().setUp()
+        vpn_agent = {'host': FAKE_HOST}
+        self.core_plugin = mock.Mock()
+        self.core_plugin.get_vpn_agents_hosting_routers.return_value = \
+            [vpn_agent]
+
+        directory.add_plugin(constants.CORE, self.core_plugin)
+        self._fake_router = FakeSqlQueryObject(
+            id=FAKE_ROUTER_ID,
+            gw_port=FakeSqlQueryObject(network_id=_uuid())
+        )
+        self.svc_plugin = mock.Mock()
+        self.svc_plugin.get_vpn_agents_hosting_routers.return_value = \
+            [vpn_agent]
+        self.svc_plugin.schedule_router.return_value = vpn_agent
+        self.svc_plugin._get_vpnservice.return_value = FakeSqlQueryObject(
+            router_id=FAKE_ROUTER_ID,
+            router=self._fake_router
+        )
+        self.svc_plugin.get_vpn_agent_on_host.return_value = {'id': FAKE_HOST}
+        self.svc_plugin.get_vpnservice.return_value = FAKE_VPNSERVICE_1
+        self.svc_plugin.get_vpnservice_router_id.return_value = FAKE_ROUTER_ID
+        self.driver = ipsec_driver.IPsecOvnVPNDriver(self.svc_plugin)
+        self.driver.make_vpnservice_dict = mock.Mock(
+            return_value={'id': FAKE_HOST})
+
+    def test_get_vpn_services_on_host(self):
+        with mock.patch('neutron_lib.context.get_admin_context') as get_ctx:
+            mock_ctx = mock.Mock()
+            mock_ctx.session.query().join().join().filter.return_value = [
+                {'id': FAKE_HOST}]
+            get_ctx.return_value = mock_ctx
+            context = n_ctx.get_admin_context()
+            driver_callback = ipsec_driver.IPsecVpnOvnDriverCallBack(
+                self.driver)
+            self.assertEqual(
+                [{'id': FAKE_HOST}],
+                driver_callback.get_vpn_services_on_host(
+                    context, FAKE_HOST)
+            )
+            self.svc_plugin.get_vpn_agent_on_host.assert_called_once_with(
+                mock.ANY, FAKE_HOST)
+            self.svc_plugin.auto_schedule_routers.assert_called_once_with(
+                mock.ANY, {'id': FAKE_HOST})