[OVN] Allow to execute MetadataProxyHandler in a local thread

If configuration option "metadata_workers=0", the OVN metadata agent
will try to spawn the ``MetadataProxyHandler`` instance inside a local
thread, instead of creating a new process. In this case, the method
``MetadataProxyHandler.post_fork_initialize`` is never called and the
SB IDL is never created.

This patch passes the OVN metadata agent SB IDL instance to the proxy
handler instance. This also reduces the number of OVN database active
connections.

Closes-Bug: #1993181
Change-Id: If9d827228002de7e3a55be660da266b60b0dfb79
(cherry picked from commit f43891b)

Author: ralonsoh

neutron/agent/ovn/metadata/agent.py

@@ -242,11 +242,6 @@ def start(self):
         self.ovs_idl = ovsdb.MetadataAgentOvsIdl().start()
         self._load_config()
 
-        # Launch the server that will act as a proxy between the VM's and Nova.
-        proxy = metadata_server.UnixDomainMetadataProxy(self.conf,
-                self.chassis)
-        proxy.run()
-
         tables = ('Encap', 'Port_Binding', 'Datapath_Binding', 'SB_Global',
                   'Chassis')
         events = (PortBindingChassisCreatedEvent(self),
@@ -272,13 +267,18 @@ def start(self):
         # Now IDL connections can be safely used.
         self._post_fork_event.set()
 
+        # Launch the server that will act as a proxy between the VM's and Nova.
+        self._proxy = metadata_server.UnixDomainMetadataProxy(
+            self.conf, self.chassis, sb_idl=self.sb_idl)
+        self._proxy.run()
+
         # Do the initial sync.
         self.sync()
 
         # Register the agent with its corresponding Chassis
         self.register_metadata_agent()
 
-        proxy.wait()
+        self._proxy.wait()
 
     @tenacity.retry(
         wait=tenacity.wait_exponential(

neutron/agent/ovn/metadata/server.py

@@ -44,10 +44,10 @@
 
 class MetadataProxyHandler(object):
 
-    def __init__(self, conf, chassis):
+    def __init__(self, conf, chassis, sb_idl):
         self.conf = conf
         self.chassis = chassis
-        self._sb_idl = None
+        self._sb_idl = sb_idl
         self._post_fork_event = threading.Event()
         self.subscribe()
 
@@ -193,9 +193,10 @@ def _sign_instance_id(self, instance_id):
 
 class UnixDomainMetadataProxy(object):
 
-    def __init__(self, conf, chassis):
+    def __init__(self, conf, chassis, sb_idl=None):
         self.conf = conf
         self.chassis = chassis
+        self.sb_idl = sb_idl
         agent_utils.ensure_directory_exists_without_file(
             cfg.CONF.metadata_proxy_socket)
 
@@ -224,7 +225,9 @@ def run(self):
         md_workers = self.conf.metadata_workers
         if md_workers is None:
             md_workers = 2
-        self.server.start(MetadataProxyHandler(self.conf, self.chassis),
+        sb_idl = self.sb_idl if md_workers == 0 else None
+        self.server.start(MetadataProxyHandler(self.conf, self.chassis,
+                                               sb_idl),
                           self.conf.metadata_proxy_socket,
                           workers=md_workers,
                           backlog=self.conf.metadata_backlog,

neutron/tests/functional/agent/ovn/metadata/test_metadata_agent.py

@@ -87,18 +87,17 @@ def _start_metadata_agent(self):
 
         ovn_sb_db = self.ovsdb_server_mgr.get_ovsdb_connection_path('sb')
         conf.set_override('ovn_sb_connection', ovn_sb_db, group='ovn')
-
-        # We don't need the HA proxy server running for now
-        p = mock.patch.object(metadata_server, 'UnixDomainMetadataProxy')
-        p.start()
-        self.addCleanup(p.stop)
+        conf.set_override('metadata_workers', '0')
 
         self.chassis_name = self.add_fake_chassis(self.FAKE_CHASSIS_HOST)
         mock.patch.object(agent.MetadataAgent,
                           '_get_own_chassis_name',
                           return_value=self.chassis_name).start()
         agt = agent.MetadataAgent(conf)
-        agt.start()
+        with mock.patch.object(metadata_server.UnixDomainMetadataProxy,
+                               'wait'):
+            agt.start()
+
         # Metadata agent will open connections to OVS and SB databases.
         # Close connections to them when the test ends,
         self.addCleanup(agt.ovs_idl.ovsdb_connection.stop)
@@ -338,3 +337,9 @@ def test__ensure_datapath_checksum_if_dpdk(self):
         else:
             self.fail('Rule not found in "mangle" table, in namespace %s' %
                       namespace)
+
+    def test_metadata_proxy_handler_idl(self):
+        # This test relies on the configuration option metadata_workers=0
+        proxy_sb_idl = self.agent._proxy.server._server._application.sb_idl
+        agent_sb_idl = self.agent.sb_idl
+        self.assertEqual(agent_sb_idl, proxy_sb_idl)

neutron/tests/unit/agent/ovn/metadata/test_server.py

@@ -55,8 +55,8 @@ def setUp(self):
         self.useFixture(self.fake_conf_fixture)
         self.log_p = mock.patch.object(agent, 'LOG')
         self.log = self.log_p.start()
-        self.handler = agent.MetadataProxyHandler(self.fake_conf, 'chassis1')
-        self.handler.sb_idl = mock.Mock()
+        self.handler = agent.MetadataProxyHandler(self.fake_conf, 'chassis1',
+                                                  mock.Mock())
         self.handler._post_fork_event.set()
 
     def test_call(self):