Standalone WSGI Containers

There are popular servers written in Python that contain WSGI applications and serve HTTP. These servers stand alone when they run; you can proxy to them from your web server. Note the section on Proxy Setups if you run into issues.

Gunicorn

Gunicorn ‘Green Unicorn’ is a WSGI HTTP Server for UNIX. It’s a pre-fork worker model ported from Ruby’s Unicorn project. It supports both eventlet and greenlet. Running a Flask application on this server is quite simple:

$ gunicorn myproject:app

Gunicorn provides many command-line options – see gunicorn -h. For example, to run a Flask application with 4 worker processes (-w 4) binding to localhost port 4000 (-b 127.0.0.1:4000):

$ gunicorn -w 4 -b 127.0.0.1:4000 myproject:app

The gunicorn command expects the names of your application module or package and the application instance within the module. If you use the application factory pattern, you can pass a call to that:

$ gunicorn "myproject:create_app()"

uWSGI

uWSGI is a fast application server written in C. It is very configurable which makes it more complicated to setup than gunicorn.

Running uWSGI HTTP Router:

$ uwsgi --http 127.0.0.1:5000 --module myproject:app

For a more optimized setup, see configuring uWSGI and NGINX.

Gevent

Gevent is a coroutine-based Python networking library that uses greenlet to provide a high-level synchronous API on top of libev event loop:

from gevent.pywsgi import WSGIServer
from yourapplication import app

http_server = WSGIServer(('', 5000), app)
http_server.serve_forever()

Twisted Web

Twisted Web is the web server shipped with Twisted, a mature, non-blocking event-driven networking library. Twisted Web comes with a standard WSGI container which can be controlled from the command line using the twistd utility:

$ twistd web --wsgi myproject.app

This example will run a Flask application called app from a module named myproject.

Twisted Web supports many flags and options, and the twistd utility does as well; see twistd -h and twistd web -h for more information. For example, to run a Twisted Web server in the foreground, on port 8080, with an application from myproject:

$ twistd -n web --port tcp:8080 --wsgi myproject.app

Proxy Setups

If you deploy your application using one of these servers behind an HTTP proxy you will need to rewrite a few headers in order for the application to work. The two problematic values in the WSGI environment usually are REMOTE_ADDR and HTTP_HOST. You can configure your httpd to pass these headers, or you can fix them in middleware. Werkzeug ships a fixer that will solve some common setups, but you might want to write your own WSGI middleware for specific setups.

Here’s a simple nginx configuration which proxies to an application served on localhost at port 8000, setting appropriate headers:

server {
    listen 80;

    server_name _;

    access_log  /var/log/nginx/access.log;
    error_log  /var/log/nginx/error.log;

    location / {
        proxy_pass         http://127.0.0.1:8000/;
        proxy_redirect     off;

        proxy_set_header   Host                 $host;
        proxy_set_header   X-Real-IP            $remote_addr;
        proxy_set_header   X-Forwarded-For      $proxy_add_x_forwarded_for;
        proxy_set_header   X-Forwarded-Proto    $scheme;
    }
}

If your httpd is not providing these headers, the most common setup invokes the host being set from X-Forwarded-Host and the remote address from X-Forwarded-For:

from werkzeug.middleware.proxy_fix import ProxyFix
app.wsgi_app = ProxyFix(app.wsgi_app, x_proto=1, x_host=1)

If you want to rewrite the headers from another header, you might want to use a fixer like this:

class CustomProxyFix(object):

    def __init__(self, app):
        self.app = app

    def __call__(self, environ, start_response):
        host = environ.get('HTTP_X_FHOST', '')
        if host:
            environ['HTTP_HOST'] = host
        return self.app(environ, start_response)

app.wsgi_app = CustomProxyFix(app.wsgi_app)