[google-appengine] Deploying Flask Socket.io application with eventlet on Google AppEngine

[Matthew Ha]

I am using flask socket.io configured with eventlet on a flexible google 
appengine instance. According to the flask socket.io documentation: 
https://flask-socketio.readthedocs.io/en/latest/ running 
`socketio.run(app)` will start a webserver if eventlet is installed. 

I have a local react web app attempting to establish a WebSocket connection 
with this app engine instance. The web app uses socket.io and initially 
defaults to polling HTTP requests. These requests all timeout-- I'm unable 
to establish a web socket connection. I'm not sure what might be causing my 
issue, whether it is my app engine configuration or my flask socket.io 
setup.

Here is my initialization code for flask socket.io:

    app = Flask(__name__)
    socketio = SocketIO(app)
    socketio.init_app(app, cors_allowed_origins="*")
    ..
    ..
    if __name__ == '__main__':
        socketio.run(app, debug=True)

    

Here is my app.yaml:

    runtime: python


    env: flex


    entrypoint: python3 server.py


    runtime_config: 
      python_version: 3


    manual_scaling:
      instances: 1


    network:
      session_affinity: true


Here is the web app code attempting to set up the connection:
    import io from 'socket.io-client'
    const socketURL = "<app-engine-instance-url>:5000"
    const socket = io.connect(socketURL)



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