"Empty reply from server" for Flask + uWSGI setup

Question

I'm getting started with WSGI and until now, with a little help from some tutorials,I'm making some tests towards Flask with uWSGI in front of it, since that Flask is not a good option for Production environments (doesn't scale well and by default, it answers one request per time - http://flask.pocoo.org/docs/0.12/deploying/) and uWSGI gives flexibility and more reliability, spawning workers and processes. Am I wrong?

Most of the tutorials that I saw until, are pointing about setups with Nginx in front of WSGI, but is it really necessary? What I'm trying to do is just to give a scalable way to deliver requests to my Flask application, something with more performance and scalability.

So I have this basic setup:

hello.py

from flask import Flask

app = Flask(__name__)

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

if __name__ == "__main__":
    app.run(host='0.0.0.0', port=8080)

wsgi.py

from hello import app

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

Running uWSGI:

uwsgi --socket 0.0.0.0:8080 --plugin python --wsgi-file wsgi.py --callable app --master --processes 4 --threads 2 &

When I perform a curl against the loopback address, I receive an empty reply..

curl http://127.0.0.1:8080
invalid request block size: 21573 (max 4096)...skip
curl: (52) Empty reply from server

Forgive me, but I can't see what I'm missing. Does anyone here, more experienced with WSGI, could point where is the failure of this setup? Any help would me much appreciated.

Reference documents: https://www.digitalocean.com/community/tutorials/how-to-serve-flask-applications-with-uwsgi-and-nginx-on-ubuntu-16-04 http://uwsgi-docs.readthedocs.io/en/latest/WSGIquickstart.html

Answer 1

Your option, socket should be used when you combine uwsgi with web server (nginx for example). Otherwise you should use http, so

uwsgi --http 0.0.0.0:8080 --plugin python --wsgi-file wsgi.py --callable app --master --processes 4 --threads 2

will work.

Production environments (doesn't scale well and by default, it answers one request per time - http://flask.pocoo.org/docs/0.12/deploying/) and uWSGI gives flexibility and more reliability, spawning workers and processes. Am I wrong?

You are right.

Most of the tutorials that I saw until, are pointing about setups with Nginx in front of WSGI, but is it really necessary? What I'm trying to do is just to give a scalable way to deliver requests to my Flask application, something with more performance and scalability.

Well, nginx is designed to be in front and having it is much better then only application server (uwsgi). Specialisation, that's the key. Let your application server focus on bussiness processing and python.