How to run Flask with Gunicorn in multithreaded mode

Question

I have web application written in Flask. As suggested by everyone, I can\'t use Flask in production. So I thought of Gunicorn with Flask.

In Flask

Answer 1

The best thing to do is to use pre-fork mode (preload_app=True). This will initialize your code in a "master" process and then simply fork off worker processes to handle requests. If you are running on linux and assuming your model is read-only, the OS is smart enough to reuse the physical memory amongst all the processes.

Answer 2

You can start your app with multiple workers or async workers with Gunicorn.

Flask server.py

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "Hello World!"

if __name__ == "__main__":
    app.run()

Gunicorn with gevent async worker

gunicorn server:app -k gevent --worker-connections 1000

Gunicorn 1 worker 12 threads:

gunicorn server:app -w 1 --threads 12

Gunicorn with 4 workers (multiprocessing):

gunicorn server:app -w 4

More information on Flask concurrency in this post: How many concurrent requests does a single Flask process receive?.