[eventlet-removal] Remove the usage of eventlet in the Neutron API

This patch removes the usage of eventlet in the Neutron API, but
only in the API process; that means the OVN maintenance worker (in case
of using ML2/OVN), the periodic worker or the RPC server are still
importing it and monkey patching the kernel libraries.

Related-Bug: #2087953
Change-Id: Icd15d8f1da02b9a2f074c00de4378bc0692a3b64

doc/source/eventlet_deprecation/index.rst

@@ -62,3 +62,30 @@ This implementation does not rely on ``neutron.api.wsgi.Server`` nor
   configuration variable. Right now only the embedded form (local thread)
   is implemented (``metadata_workers=0``, the default value). Future
   implementations will enable again this configuration variable.
+
+
+Neutron API
+-----------
+
+The Neutron API currently can be executed only with the uWSGI module; the
+eventlet executor has been deprecated, although the code has not been removed
+from the repository yet.
+
+The Neutron API consists of the following executables:
+
+* The API server: is a multiprocess worker; each process is created by the
+  ``uWSGI`` server.
+
+* The periodic worker: a mult process worker that spawns several threads to
+  execute the periodic workers.
+
+* The RPC worker: a multiprocess process worker that attends the requests from
+  the RPC clients, for example the Neutron agents.
+
+* The ML2/OVN maintenance worker: single process worker, needed by the ML2/OVN
+  mechanism driver.
+
+
+.. note::
+
+  Right now, only the API server is running without eventlet.

neutron/cmd/eventlet/server/__init__.py

@@ -11,7 +11,6 @@
 #    under the License.
 
 from neutron import server
-from neutron.server import api_eventlet
 from neutron.server import ovn_maintenance
 from neutron.server import periodic_eventlet
 from neutron.server import rpc_eventlet
@@ -26,10 +25,6 @@ def main_rpc_eventlet():
     server.boot_server(rpc_eventlet.eventlet_rpc_server)
 
 
-def main_api_eventlet():
-    return server.boot_server(api_eventlet.eventlet_api_server)
-
-
 def main_periodic_eventlet():
     server.boot_server(periodic_eventlet.eventlet_periodic_workers)
 

neutron/cmd/server/__init__.py

@@ -0,0 +1,21 @@
+# Copyright (c) 2025 Red Hat Inc.
+# All rights reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from neutron import server
+from neutron.server import api
+
+
+def main_api_uwsgi():
+    return server.boot_server(api.api_server)

neutron/server/api.py

@@ -24,7 +24,7 @@ from neutron.common import config
 from neutron.common import profiler
 
 
-def eventlet_api_server():
+def api_server():
     profiler.setup('neutron-server', cfg.CONF.host)
     app = config.load_paste_app('neutron')
     registry.publish(resources.PROCESS, events.BEFORE_SPAWN,

neutron/wsgi/api.py

@@ -22,10 +22,10 @@ eventlet_utils.monkey_patch()
 import threading  # noqa:E402
 
 from neutron import server  # noqa:E402
-from neutron.server import api_eventlet  # noqa:E402
+from neutron.server import api  # noqa:E402
 
 application = None
 lock = threading.Lock()
 with lock:
     if application is None:
-        application = server.boot_server(api_eventlet.eventlet_api_server)
+        application = server.boot_server(api.api_server)

setup.cfg

@@ -31,7 +31,7 @@ data_files =
 
 [entry_points]
 wsgi_scripts =
-    neutron-api = neutron.cmd.eventlet.server:main_api_eventlet
+    neutron-api = neutron.cmd.server:main_api_uwsgi
 console_scripts =
     neutron-db-manage = neutron.db.migration.cli:main
     neutron-dhcp-agent = neutron.cmd.eventlet.agents.dhcp:main