Gunicorn and eventlet error

[jonyr]

Hi Miguel, I'm developing a Flask Rest API. I'm trying to use web sockets to push messages from backend to frontend.
I can run the project locally, and everything works fine. But when I try to use Gunicorn to start up the project, the project does not work properly.

This is my code / entry point

wsgi.py file

#pylint: disable=wrong-import-position, wrong-import-order
import eventlet

eventlet.monkey_patch()

import os
import time

from flask import g, request
from flask_socketio import SocketIO

from app import create_app, db

app = create_app(os.environ.get("FLASK_ENV", 'development'))
socketio = SocketIO(app, async_mode='eventlet')

if __name__ == '__main__':
    socketio.run(app, host="0.0.0.0", port=5000, debug=True, use_reloader=True, log_output=True)

Running locally

export FLASK_ENV=development
export FLASK_APP=wsgi.py
export DEBUG=1

python wsgi.py

Terminal output

Server initialized for eventlet.
 * Restarting with stat
Server initialized for eventlet.
 * Debugger is active!
 * Debugger PIN: 124-101-814
(73886) wsgi starting up on http://0.0.0.0:5000

But when I try to use Gunicorn as it is described here

 gunicorn -k eventlet -w 1 wsgi:app -b :5000

Terminal output

[2021-06-07 19:26:26 -0300] [74095] [INFO] Starting gunicorn 20.1.0
[2021-06-07 19:26:26 -0300] [74095] [INFO] Listening at: http://0.0.0.0:5000 (74095)
[2021-06-07 19:26:26 -0300] [74095] [INFO] Using worker: eventlet
[2021-06-07 19:26:26 -0300] [74097] [INFO] Booting worker with pid: 74097
Server initialized for eventlet.
Traceback (most recent call last):
  File "/home/jony/flask_app/venv/lib/python3.8/site-packages/eventlet/hubs/hub.py", line 476, in fire_timers
    timer()
  File "/home/jony/flask_app/venv/lib/python3.8/site-packages/eventlet/hubs/timer.py", line 59, in __call__
    cb(*args, **kw)
  File "/home/jony/flask_app/venv/lib/python3.8/site-packages/eventlet/greenthread.py", line 221, in main
    result = function(*args, **kwargs)
  File "/home/jony/flask_app/venv/lib/python3.8/site-packages/gunicorn/workers/geventlet.py", line 78, in _eventlet_serve
    conn, addr = sock.accept()
  File "/home/jony/flask_app/venv/lib/python3.8/site-packages/eventlet/greenio/base.py", line 230, in accept
    self._trampoline(fd, read=True, timeout=self.gettimeout(), timeout_exc=_timeout_exc)
  File "/home/jony/flask_app/venv/lib/python3.8/site-packages/eventlet/greenio/base.py", line 208, in _trampoline
    return trampoline(fd, read=read, write=write, timeout=timeout,
  File "/home/jony/flask_app/venv/lib/python3.8/site-packages/eventlet/hubs/__init__.py", line 155, in trampoline
    listener = hub.add(hub.READ, fileno, current.switch, current.throw, mark_as_closed)
  File "/home/jony/flask_app/venv/lib/python3.8/site-packages/eventlet/hubs/kqueue.py", line 53, in add
    self._control([event], 0, 0)
  File "/home/jony/flask_app/venv/lib/python3.8/site-packages/eventlet/hubs/kqueue.py", line 39, in _control
    return self.kqueue.control(events, max_events, timeout)
OSError: [Errno 9] Bad file descriptor
[2021-06-07 19:26:27 -0300] [74097] [ERROR] Exception in worker process

Any idea, what I'm doing wrong?

Thanks in advance,
Juan R

Let me attach my requirements.txt, in case it helps.
requirements.txt

[miguelgrinberg]

I honestly don't know what's wrong. The error comes from eventlet, it does not have anything to do with this package, so I don't think this is caused by something you've done wrong. The best I can suggest is that you try different versions of eventlet. There are a couple that are newer than the one you are using, but if those don't work either you should also try older releases.

[jonyr]

Miguel, thanks for you honest answer.
I've tried to downgrade eventlet package version, but until now without success.
Should I try gevent instead of eventlet?

Thanks again Miguel

[miguelgrinberg]

@jonyr You can try gevent if you like, sure. You can also run Gunicorn without eventlet/gevent.

[jonyr]

@miguelgrinberg how websockets will be managed on a prod environment running gunicorn without eventlet/gevent as you mention? Thanks

[miguelgrinberg]

@jonyr See the 3rd option in the Gunicorn section of the docs.

[jonyr]

@miguelgrinberg I will try.
I really appreciate your help with all this answers.