There are popular servers written in Python that allow the execution of WSGI applications as well. These servers stand alone when they run; you can proxy to them from your web server.
Tornado is an open source version of the scalable, non-blocking web server and tools that power FriendFeed. Because it is non-blocking and uses epoll, it can handle thousands of simultaneous standing connections, which means it is ideal for real-time web services. Integrating this service with Flask is a trivial task:
from tornado.wsgi import WSGIContainer from tornado.httpserver import HTTPServer from tornado.ioloop import IOLoop from yourapplication import app http_server = HTTPServer(WSGIContainer(app)) http_server.listen(5000) IOLoop.instance().start()
from gevent.wsgi import WSGIServer from yourapplication import app http_server = WSGIServer(('', 5000), app) http_server.serve_forever()
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 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
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. Werkzeug ships a fixer that will solve some common setups, but you might want to write your own WSGI middleware for specific setups.
The most common setup invokes the host being set from X-Forwarded-Host and the remote address from X-Forwarded-For:
from werkzeug.contrib.fixers import ProxyFix app.wsgi_app = ProxyFix(app.wsgi_app)
Please keep in mind that it is a security issue to use such a middleware in a non-proxy setup because it will blindly trust the incoming headers which might be forged by malicious clients.
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)