Gevent/Gevent-websocket not being used by Flask-SocketIO

Question

I am building a web interface/data API using Flask and Flask-SocketIO for websocket communication. I would like to start shifting to a more development-ready setup using Gevent/Gevent-websocket, Gunicorn, and eventually Nginx for load balancing. However, after installing Gevent and Gevent-websocket, I am still getting a warning message when starting the SocketIO server:

WebSocket transport not available. Install eventlet or gevent and gevent-websocket for improved performance.

According to the Flask-SocketIO docs,

When the application is in debug mode the Werkzeug development server is still used and configured properly inside socketio.run(). In production mode the eventlet web server is used if available, else the gevent web server is used. If eventlet and gevent are not installed, the Werkzeug development web server is used.

This implies that the use of Gevent should be automated behind the scenes as part of Flask-SocketIO. I checked my Python installs with pip list and confirmed that I have Gevent 1.3.4 and Gevent-websocket 0.10.1 installed. Here is the initialization code for the SocketIO server:

app.py

flaskApp = Flask(__name__)
flaskApp.config['SESSION_TYPE'] = 'filesystem'
Session(flaskApp)
socketio = SocketIO(flaskApp, async_mode='threading', manage_session=False)

def createApp():
    flaskApp.secret_key = "super secret"
    socketio.run(flaskApp, host='0.0.0.0', port=80)

start.py

app.register_blueprint(monitor.blueprint)
...
createApp()

Why is Flask-SocketIO not detecting my Gevent install?

Miguel Miguel · Accepted Answer · 2018-07-15T16:30:36

The portion of the docs that you quoted refers to the async_mode argument, and how it is set by default. You are setting async_mode='threading', so that disables the automatic selection of an async mode. Remove the argument, and then you'll get eventlet or gevent, depending on what you have installed.

Gevent/Gevent-websocket not being used by Flask-SocketIO

1 Answers