Why Gevent On A Flask App With Apache + Mod_wsgi Is Raising Notimplementederror?

I'm having an issue deploying my Flask app with Apache (mod_wsgi) and gevent on a shared hosting (Webfaction). The application works fine in the development server provided by Flas

Solution 1:

It seems like i found the solution myself. The following directive solved my issue:

WSGIApplicationGroup %{GLOBAL}

The idea comes from another answer where it is suggested to set WSGIApplicationGroup to GLOBAL to solve a problem with a WSGI process that keep crashing. From WSGI documentation:

To force a specific WSGI application to be run within the very first Python sub interpreter created when Python is initialised, the WSGIApplicationGroup directive should be used and the group set to '%{GLOBAL}'.

Cannot fully understand why this directive solve my issue but it does. I will be more than happy if someone is able to explain this to me in plain English ;-)

Solution 2:

Try replacing monkey.patch_all() with monkey.patch_all(thread=False). If it's really the threading module which is causing the trouble when patched, this should solve it. request does not use threading.

Solution 3:

I posted below answer on https://serverfault.com/a/869625/355861

apache mod_wsgi is not currently compatible with gevent. For AWS elastic beanstalk with Apache, I used async_mode="threading" for Flask and it works well. Note, threading has less performance than gevent. https://flask-socketio.readthedocs.io/en/latest/#deployment

app = Flask(__name__,static_folder='static')
socketio = SocketIO(app, async_mode="threading") 

Note that Flask can run standalone with gevent.

app = Flask(__name__,static_folder='static')
socketio = SocketIO(app, async_mode="gevent") 

if__name__== '__main__':
    HOST = '127.0.0.1'
    PORT = 5055
    socketio.run(app, port=PORT, host=HOST)

However, you really want an HTTP server in front of it such as Gunicorn.