Deployment Options ================== Depending on what you have available there are multiple ways to run Flask applications. A very common method is to use the builtin server during development and maybe behind a proxy for simple applications, but there are more options available. If you have a different WSGI server look up the server documentation about how to use a WSGI app with it. Just remember that your application object is the actual WSGI application. FastCGI ------- A very popular deployment setup on servers like `lighttpd`_ and `nginx`_ is FastCGI. To use your WSGI application with any of them you will need a FastCGI server first. The most popular one is `flup`_ which we will use for this guide. Make sure to have it installed. Creating a `.fcgi` file ``````````````````````` First you need to create the FastCGI server file. Let's call it `yourapplication.fcgi`:: #!/usr/bin/python from flup.server.fcgi import WSGIServer from yourapplication import app WSGIServer(app).run() This is enough for Apache to work, however lighttpd and nginx need a socket to communicate with the FastCGI server. For that to work you need to pass the path to the socket to the :class:`~flup.server.fcgi.WSGIServer`:: WSGIServer(application, bindAddress='/path/to/fcgi.sock').run() The path has to be the exact same path you define in the server config. Save the `yourapplication.fcgi` file somewhere you will find it again. It makes sense to have that in `/var/www/yourapplication` or something similar. Make sure to set the executable bit on that file so that the servers can execute it:: # chmod +x /var/www/yourapplication/yourapplication.fcgi Configuring lighttpd ```````````````````` A basic FastCGI configuration for lighttpd looks like that:: fastcgi.server = ("/yourapplication" => "yourapplication" => ( "socket" => "/tmp/yourapplication-fcgi.sock", "bin-path" => "/var/www/yourapplication/yourapplication.fcgi", "check-local" => "disable" ) ) This configuration binds the application to `/yourapplication`. If you want the application to work in the URL root you have to work around a lighttpd bug with the :class:`~werkzeug.contrib.fixers.LighttpdCGIRootFix` middleware. Make sure to apply it only if you are mounting the application the URL root. Configuring nginx ````````````````` Installing FastCGI applications on nginx is a bit tricky because by default some FastCGI parameters are not properly forwarded. A basic FastCGI configuration for nginx looks like this:: location /yourapplication/ { include fastcgi_params; if ($uri ~ ^/yourapplication/(.*)?) { set $path_url $1; } fastcgi_param PATH_INFO $path_url; fastcgi_param SCRIPT_NAME /yourapplication; fastcgi_pass unix:/tmp/yourapplication-fcgi.sock; } This configuration binds the application to `/yourapplication`. If you want to have it in the URL root it's a bit easier because you don't have to figure out how to calculate `PATH_INFO` and `SCRIPT_NAME`:: location /yourapplication/ { include fastcgi_params; fastcgi_param PATH_INFO $fastcgi_script_name; fastcgi_param SCRIPT_NAME ""; fastcgi_pass unix:/tmp/yourapplication-fcgi.sock; } Since Nginx doesn't load FastCGI apps, you have to do it by yourself. You can either write an `init.d` script for that or execute it inside a screen session:: $ screen $ /var/www/yourapplication/yourapplication.fcgi Debugging ````````` FastCGI deployments tend to be hard to debug on most webservers. Very often the only thing the server log tells you is something along the lines of "premature end of headers". In order to debug the application the only thing that can really give you ideas why it breaks is switching to the correct user and executing the application by hand. This example assumes your application is called `application.fcgi` and that your webserver user is `www-data`:: $ su www-data $ cd /var/www/yourapplication $ python application.fcgi Traceback (most recent call last): File "yourapplication.fcg", line 4, in ImportError: No module named yourapplication In this case the error seems to be "yourapplication" not being on the python path. Common problems are: - relative paths being used. Don't rely on the current working directory - the code depending on environment variables that are not set by the web server. - different python interpreters being used. .. _lighttpd: http://www.lighttpd.net/ .. _nginx: http://nginx.net/ .. _flup: http://trac.saddi.com/flup mod_wsgi (Apache) ----------------- If you are using the `Apache`_ webserver you should consider using `mod_wsgi`_. .. _Apache: http://httpd.apache.org/ Installing `mod_wsgi` ````````````````````` If you don't have `mod_wsgi` installed yet you have to either install it using a package manager or compile it yourself. The mod_wsgi `installation instructions`_ cover installation instructions for source installations on UNIX systems. If you are using ubuntu / debian you can apt-get it and activate it as follows:: # apt-get install libapache2-mod-wsgi On FreeBSD install `mod_wsgi` by compiling the `www/mod_wsgi` port or by using pkg_add:: # pkg_add -r mod_wsgi If you are using pkgsrc you can install `mod_wsgi` by compiling the `www/ap2-wsgi` package. If you encounter segfaulting child processes after the first apache reload you can safely ignore them. Just restart the server. Creating a `.wsgi` file ``````````````````````` To run your application you need a `yourapplication.wsgi` file. This file contains the code `mod_wsgi` is executing on startup to get the application object. The object called `application` in that file is then used as application. For most applications the following file should be sufficient:: from yourapplication import app as application If you don't have a factory function for application creation but a singleton instance you can directly import that one as `application`. Store that file somewhere where you will find it again (eg: `/var/www/yourapplication`) and make sure that `yourapplication` and all the libraries that are in use are on the python load path. If you don't want to install it system wide consider using a `virtual python`_ instance. Configuring Apache `````````````````` The last thing you have to do is to create an Apache configuration file for your application. In this example we are telling `mod_wsgi` to execute the application under a different user for security reasons: .. sourcecode:: apache ServerName example.com WSGIDaemonProcess yourapplication user=user1 group=group1 processes=1 threads=5 WSGIScriptAlias / /var/www/yourapplication/yourapplication.wsgi WSGIProcessGroup yourapplication WSGIApplicationGroup %{GLOBAL} Order deny,allow Allow from all For more information consult the `mod_wsgi wiki`_. .. _mod_wsgi: http://code.google.com/p/modwsgi/ .. _installation instructions: http://code.google.com/p/modwsgi/wiki/QuickInstallationGuide .. _virtual python: http://pypi.python.org/pypi/virtualenv .. _mod_wsgi wiki: http://code.google.com/p/modwsgi/wiki/ Tornado -------- `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() .. _Tornado: http://www.tornadoweb.org/ .. _FriendFeed: http://friendfeed.com/ Gevent ------- `Gevent`_ is a coroutine-based Python networking library that uses `greenlet`_ to provide a high-level synchronous API on top of `libevent`_ event loop:: from gevent.wsgi import WSGIServer from yourapplication import app http_server = WSGIServer(('', 5000), app) http_server.serve_forever() .. _Gevent: http://www.gevent.org/ .. _greenlet: http://codespeak.net/py/0.9.2/greenlet.html .. _libevent: http://monkey.org/~provos/libevent/ CGI --- If all other deployment methods do not work, CGI will work for sure. CGI is supported by all major browsers but usually has a less-than-optimal performance. This is also the way you can use a Flask application on Google's `AppEngine`_, there however the execution does happen in a CGI-like environment. The application's performance is unaffected because of that. .. _AppEngine: http://code.google.com/appengine/ Creating a `.cgi` file `````````````````````` First you need to create the CGI application file. Let's call it `yourapplication.cgi`:: #!/usr/bin/python from wsgiref.handlers import CGIHandler from yourapplication import app CGIHandler().run(app) If you're running Python 2.4 you will need the :mod:`wsgiref` package. Python 2.5 and higher ship this as part of the standard library. Server Setup ```````````` Usually there are two ways to configure the server. Either just copy the `.cgi` into a `cgi-bin` (and use `mod_rerwite` or something similar to rewrite the URL) or let the server point to the file directly. In Apache for example you can put a like like this into the config: .. sourcecode:: apache ScriptName /app /path/to/the/application.cgi For more information consult the documentation of your webserver.