Change metadata-agent to spawn multiple workers

There is currently only one metadata-agent per network node,
which could be handling connections from hundreds or thousands
of metadata-namespace-proxy processes.

This change addes a new "metadata_workers = XX" to the ini file
to support creating more workers to help improve performance.

Change-Id: Ib9ebcfc543a83982dd93db79c7dc631283fd3bfa
Partial-bug: #1274536

etc/metadata_agent.ini

@@ -26,3 +26,6 @@ admin_password = %SERVICE_PASSWORD%
 
 # Location of Metadata Proxy UNIX domain socket
 # metadata_proxy_socket = $state_path/metadata_proxy
+
+# Number of separate worker processes for metadata server
+# metadata_workers = 0

neutron/agent/metadata/agent.py

@@ -37,6 +37,7 @@ from neutron.common import utils
 from neutron import context
 from neutron.openstack.common import log as logging
 from neutron.openstack.common import loopingcall
+from neutron.openstack.common import service
 from neutron import wsgi
 
 LOG = logging.getLogger(__name__)
@@ -192,12 +193,34 @@ class UnixDomainHttpProtocol(eventlet.wsgi.HttpProtocol):
                                             server)
 
 
+class WorkerService(wsgi.WorkerService):
+    def start(self):
+        self._server = self._service.pool.spawn(self._service._run,
+                                                self._application,
+                                                self._service._socket)
+
+
 class UnixDomainWSGIServer(wsgi.Server):
-    def start(self, application, file_socket, backlog=128):
-        sock = eventlet.listen(file_socket,
+    def __init__(self, name):
+        self._socket = None
+        self._launcher = None
+        self._server = None
+        super(UnixDomainWSGIServer, self).__init__(name)
+
+    def start(self, application, file_socket, workers, backlog=128):
+        self._socket = eventlet.listen(file_socket,
                                        family=socket.AF_UNIX,
                                        backlog=backlog)
-        self.pool.spawn_n(self._run, application, sock)
+        if workers < 1:
+            # For the case where only one process is required.
+            self._server = self.pool.spawn_n(self._run, application,
+                                             self._socket)
+        else:
+            # Minimize the cost of checking for child exit by extending the
+            # wait interval past the default of 0.01s.
+            self._launcher = service.ProcessLauncher(wait_interval=1.0)
+            self._server = WorkerService(self, application)
+            self._launcher.launch_service(self._server, workers=workers)
 
     def _run(self, application, socket):
         """Start a WSGI service in a new green thread."""
@@ -213,7 +236,11 @@ class UnixDomainMetadataProxy(object):
     OPTS = [
         cfg.StrOpt('metadata_proxy_socket',
                    default='$state_path/metadata_proxy',
-                   help=_('Location for Metadata Proxy UNIX domain socket'))
+                   help=_('Location for Metadata Proxy UNIX domain socket')),
+        cfg.IntOpt('metadata_workers',
+                   default=0,
+                   help=_('Number of separate worker processes for metadata '
+                          'server'))
     ]
 
     def __init__(self, conf):
@@ -271,7 +298,8 @@ class UnixDomainMetadataProxy(object):
     def run(self):
         server = UnixDomainWSGIServer('neutron-metadata-agent')
         server.start(MetadataProxyHandler(self.conf),
-                     self.conf.metadata_proxy_socket)
+                     self.conf.metadata_proxy_socket,
+                     workers=self.conf.metadata_workers)
         server.wait()
 
 

neutron/tests/unit/test_metadata_agent.py

@@ -275,7 +275,7 @@ class TestUnixDomainWSGIServer(base.BaseTestCase):
     def test_start(self):
         mock_app = mock.Mock()
         with mock.patch.object(self.server, 'pool') as pool:
-            self.server.start(mock_app, '/the/path')
+            self.server.start(mock_app, '/the/path', workers=0)
             self.eventlet.assert_has_calls([
                 mock.call.listen(
                     '/the/path',
@@ -289,6 +289,22 @@ class TestUnixDomainWSGIServer(base.BaseTestCase):
                 self.eventlet.listen.return_value
             )
 
+    @mock.patch('neutron.openstack.common.service.ProcessLauncher')
+    def test_start_multiple_workers(self, process_launcher):
+        launcher = process_launcher.return_value
+
+        mock_app = mock.Mock()
+        self.server.start(mock_app, '/the/path', workers=2)
+        launcher.running = True
+        launcher.launch_service.assert_called_once_with(self.server._server,
+                                                        workers=2)
+
+        self.server.stop()
+        self.assertFalse(launcher.running)
+
+        self.server.wait()
+        launcher.wait.assert_called_once_with()
+
     def test_run(self):
         with mock.patch.object(agent, 'logging') as logging:
             self.server._run('app', 'sock')
@@ -313,6 +329,7 @@ class TestUnixDomainMetadataProxy(base.BaseTestCase):
         self.looping_mock = looping_call_p.start()
         self.addCleanup(mock.patch.stopall)
         self.cfg.CONF.metadata_proxy_socket = '/the/path'
+        self.cfg.CONF.metadata_workers = 0
 
     def test_init_doesnot_exists(self):
         with mock.patch('os.path.isdir') as isdir:
@@ -376,7 +393,7 @@ class TestUnixDomainMetadataProxy(base.BaseTestCase):
                         server.assert_has_calls([
                             mock.call('neutron-metadata-agent'),
                             mock.call().start(handler.return_value,
-                                              '/the/path'),
+                                              '/the/path', workers=0),
                             mock.call().wait()]
                         )