Standalone WSGI Servers ======================= Most WSGI servers also provide HTTP servers, so they can run a WSGI application and make it available externally. It may still be a good idea to run the server behind a dedicated HTTP server such as Apache or Nginx. See :ref:`deploying-proxy-setups` if you run into issues with that. Gunicorn -------- `Gunicorn`_ is a WSGI and HTTP server for UNIX. To run a Flask application, tell Gunicorn how to import your Flask app object. .. code-block:: text $ gunicorn -w 4 -b 0.0.0.0:5000 your_project:app The ``-w 4`` option uses 4 workers to handle 4 requests at once. The ``-b 0.0.0.0:5000`` serves the application on all interfaces on port 5000. Gunicorn provides many options for configuring the server, either through a configuration file or with command line options. Use ``gunicorn --help`` or see the docs for more information. The command expects the name of your module or package to import and the application instance within the module. If you use the application factory pattern, you can pass a call to that. .. code-block:: text $ gunicorn -w 4 -b 0.0.0.0:5000 "myproject:create_app()" Async with Gevent or Eventlet ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The default sync worker is appropriate for many use cases. If you need asynchronous support, Gunicorn provides workers using either `gevent`_ or `eventlet`_. This is not the same as Python's ``async/await``, or the ASGI server spec. When using either gevent or eventlet, greenlet>=1.0 is required, otherwise context locals such as ``request`` will not work as expected. When using PyPy, PyPy>=7.3.7 is required. To use gevent: .. code-block:: text $ gunicorn -k gevent -b 0.0.0.0:5000 your_project:app To use eventlet: .. code-block:: text $ gunicorn -k eventlet -b 0.0.0.0:5000 your_project:app .. _Gunicorn: https://gunicorn.org/ .. _gevent: http://www.gevent.org/ .. _eventlet: https://eventlet.net/ .. _greenlet: https://greenlet.readthedocs.io/en/latest/ uWSGI ----- `uWSGI`_ is a fast application server written in C. It is very configurable, which makes it more complicated to setup than Gunicorn. It also provides many other utilities for writing robust web applications. To run a Flask application, tell Gunicorn how to import your Flask app object. .. code-block:: text $ uwsgi --master -p 4 --http 0.0.0.0:5000 -w your_project:app The ``-p 4`` option uses 4 workers to handle 4 requests at once. The ``--http 0.0.0.0:5000`` serves the application on all interfaces on port 5000. uWSGI has optimized integration with Nginx and Apache instead of using a standard HTTP proxy. See :doc:`configuring uWSGI and Nginx `. Async with Gevent ~~~~~~~~~~~~~~~~~ The default sync worker is appropriate for many use cases. If you need asynchronous support, uWSGI provides workers using `gevent`_. It also supports other async modes, see the docs for more information. This is not the same as Python's ``async/await``, or the ASGI server spec. When using gevent, greenlet>=1.0 is required, otherwise context locals such as ``request`` will not work as expected. When using PyPy, PyPy>=7.3.7 is required. .. code-block:: text $ uwsgi --master --gevent 100 --http 0.0.0.0:5000 -w your_project:app .. _uWSGI: https://uwsgi-docs.readthedocs.io/en/latest/ Gevent ------ Prefer using `Gunicorn`_ with Gevent workers rather than using Gevent directly. Gunicorn provides a much more configurable and production-tested server. See the section on Gunicorn above. `Gevent`_ allows writing asynchronous, coroutine-based code that looks like standard synchronous Python. It uses `greenlet`_ to enable task switching without writing ``async/await`` or using ``asyncio``. It provides a WSGI server that can handle many connections at once instead of one per worker process. `Eventlet`_, described below, is another library that does the same thing. Certain dependencies you have, or other consideration, may affect which of the two you choose to use To use gevent to serve your application, import its ``WSGIServer`` and use it to run your ``app``. .. code-block:: python from gevent.pywsgi import WSGIServer from your_project import app http_server = WSGIServer(("", 5000), app) http_server.serve_forever() Eventlet -------- Prefer using `Gunicorn`_ with Eventlet workers rather than using Eventlet directly. Gunicorn provides a much more configurable and production-tested server. See the section on Gunicorn above. `Eventlet`_ allows writing asynchronous, coroutine-based code that looks like standard synchronous Python. It uses `greenlet`_ to enable task switching without writing ``async/await`` or using ``asyncio``. It provides a WSGI server that can handle many connections at once instead of one per worker process. `Gevent`_, described above, is another library that does the same thing. Certain dependencies you have, or other consideration, may affect which of the two you choose to use To use eventlet to serve your application, import its ``wsgi.server`` and use it to run your ``app``. .. code-block:: python import eventlet from eventlet import wsgi from your_project import app wsgi.server(eventlet.listen(("", 5000), app) 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: .. code-block:: text $ 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``: .. code-block:: text $ twistd -n web --port tcp:8080 --wsgi myproject.app .. _Twisted: https://twistedmatrix.com/trac/ .. _Twisted Web: https://twistedmatrix.com/trac/wiki/TwistedWeb .. _deploying-proxy-setups: 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: .. sourcecode:: nginx 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) .. admonition:: Trusting Headers 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)