Flask SocketIO Gunicorn Multiple Workers behind NGINX with Message Queue, correct understanding?

[spmsh]

Hi @miguelgrinberg, we are currently running our app with gunicon and eventlet (gunicorn --worker-class eventlet -w 1 module:app) behind a nginx reverse proxy. All is well except we feel 1 worker might not be enough performance wise and need to increase the number.

Looking at the documentation, Deployment Section, (https://flask-socketio.readthedocs.io/en/latest/deployment.html), if I understand correctly, adding a message queue would allow to run multiple workers together.

Doest that mean

1. we would be able to run multiple gunicorn -w 1 (because gunicorn does not support sicky sessions),
2. or we could run it with 2 or more workers (i.e., gunicorn -w 2).

If the answer is 1, then I assume all the different gunicorn -w 1 workers could be hosted on different machines as well as long as our NGINX is well configured.

Thanks for confirming our understanding and thanks again for the great lib.

[miguelgrinberg]

Option 1 is preferred, because it is fully compatible with the Socket.IO protocol. You can run multiple Gunicorn processes all on the same machine, each listening on a different port. Normally you'd want at least as many server processes as you have CPUs.

Option 2 can work too, but it is incompatible with the long-polling transport of Socket.IO. As long as you configure all your clients to connect directly through the WebSocket transport everything should work well, but long-polling clients will get 400 errors and will be unable to connect. In this case you will still need the message queue, but you can run a single Gunicorn server with multiple workers, probably as many as you have CPUs or more.

[spmsh]

got it thank you. Gunicorn's documentation suggests that for optimal performance the number of workers can be calculated as 2 * num_cpus + 1 so we'll go for that option 1 and popup Gunicorn processes according to that guidelines.