Bare minimal flup fastcgi server not working with Nginx

Question

I have written a bare minimal Python fastcgi script webapp.py for test:

#!/usr/bin/env python3
# -*- coding: UTF-8 -*-

import sys, os, traceback
from html import escape
from flup.server.fcgi import WSGIServer

def app(environ, start_response):
    start_response('200 OK', [('Content-Type', 'text/html')])
    yield 'hello world'

WSGIServer(app, bindAddress=('127.0.0.1',3001)).run()

I can start the script ./webapp.py no problem. I can also establish connection to localhost:3001 with telnet.

I then create an Nginx default configuration like this:

server {
    listen 80 default_server;
    listen [::]:80 default_server;
    root /var/www/html;
    server_name _;
    location / {
        fastcgi_param REQUEST_METHOD $request_method;
        fastcgi_param QUERY_STRING $query_string;
        fastcgi_param CONTENT_TYPE $content_type;
        fastcgi_param CONTENT_LENGTH $content_length;
        fastcgi_param GATEWAY_INTERFACE CGI/1.1;
        fastcgi_param SERVER_SOFTWARE nginx/$nginx_version;
        fastcgi_param REMOTE_ADDR $remote_addr;
        fastcgi_param REMOTE_PORT $remote_port;
        fastcgi_param SERVER_ADDR $server_addr;
        fastcgi_param SERVER_PORT $server_port;
        fastcgi_param SERVER_NAME $server_name;
        fastcgi_param SERVER_PROTOCOL $server_protocol;
        fastcgi_param SCRIPT_FILENAME $fastcgi_script_name;
        fastcgi_param PATH_INFO $fastcgi_script_name;
        fastcgi_pass localhost:3001;
    }
}

With this bare minimal configuration on my local machine, I started nginx and try to access the http://localhost . Nginx default site fails (502 Bad Gateway). In the log message, I can only see error like this repeatedly:

2017/01/05 01:23:07 [error] 30464#30464: *3 upstream prematurely closed connection while reading response header from upstream, client: 127.0.0.1, server: _, request: "GET / HTTP/1.1", upstream: "fastcgi://127.0.0.1:3001", host: "localhost"

What is going wrong with my settings or code?

Answer 1

My Mistake

If you, like I did, followed the Python3 official HOWTO: Use Python in the web , installed flup-py3 1.0.2-1 and got confused. Don't be. It is not your mistake.

There is nothing wrong with the code and settings above. The issue was how I installed flup-py3. This is how I installed it:

sudo pip3 install flup-py3

which you SHOULD NOT do.

The Solution

The answer to your question (and mine) is simple. The "stable" version 1.0.2-1 doesn't work on Python 3 at all. So the official HOWTO fxxked up in a big way.

Until the official stable version on pypi is updated, you should install your flup-py3 by either:

sudo pip3 install hg+https://hg.saddi.com/flup-py3.0/#egg=flup-py3

or:

sudo pip3 install git+https://github.com/pquentin/flup-py3.git#egg=flup-py3

The first one (hg) would be the development version of flup-py3 of the original developer Allan Saddi. While the second one (github version) is a copy created by Quentin Pradet . Both source include patches in 2012 - 2014 that fixes flup's compatibility issue.

Related Link

• Official hg mercurial repository by Allan Saddi
• Github repository by Quentin Pradet

Updates 2018 **

The latest version of flup-py3 (>=1.0.3) has already fixed this issue. You can install that with pip normally.