Nginx + socketio: events not arriving

Question

I want to send events to a flask server with socket io. But when I deploy my app via an nxginx proxy, the events don't arrive.

My Flask server app.py looks like this:

from flask_socketio import SocketIO

app = Flask(__name__)
app.config['SECRET_KEY'] = 'secret!'
socketio = SocketIO(app)

@app.route('/')
def index():
    return "this is the index function"

@socketio.on('message')
def handle_message(message):
    print('received message: ' + message)

if __name__ == '__main__':
    socketio.run(app,debug=True)

Events are sent from the client like this:

 var socket = io('http://my.ip.address.it');
 ...
 socket.emit('message', 'here is my message 1');

This works when I deploy my server on localhost. But when I deploy it on a EC2 instance, via nginx, events emitted form a client only occasionally arrive.

My nginx proxy config looks like this:

server {
    listen 80;
    server_name my.ip.add.it;

    location / {
        include proxy_params;
        proxy_pass http://127.0.0.1:8000;
    }

    location /socket.io {
        include proxy_params;
        proxy_http_version 1.1;
        proxy_buffering off;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
        proxy_pass http://127.0.0.1:8000/socket.io;
    }
}

And I start my server app like this:

gunicorn app:app -b 127.0.0.1:8000

How can I setup my Flask server correctly?

Answer 1

You need to add the Socket.IO configuration to nginx. See https://flask-socketio.readthedocs.io/en/latest/#using-nginx-as-a-websocket-reverse-proxy for the details, but here is the example from that link:

server {
    listen 80;
    server_name _;

    location / {
        include proxy_params;
        proxy_pass http://127.0.0.1:5000;
    }

    location /socket.io {
        include proxy_params;
        proxy_http_version 1.1;
        proxy_buffering off;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
        proxy_pass http://127.0.0.1:5000/socket.io;
    }
}