What Is mod_wsgi?¶
The aim of mod_wsgi is to implement a simple to use Apache module which can host any Python application which supports the Python WSGI
interface. The module would be suitable for use in hosting high
performance production web sites, as well as your average self managed
personal sites running on web hosting services.
Modes Of Operation¶
When
hosting WSGI applications using mod_wsgi, one of two primary modes of
operation can be used. In 'embedded' mode, mod_wsgi works in a similar
way to mod_python in that the Python application code will be executed
within the context of the normal Apache child processes. WSGI
applications when run in this mode will therefore share the same
processes as other Apache hosted applications using Apache modules for
PHP and Perl.
An alternate mode of operation available with
Apache 2.X on UNIX is 'daemon' mode. This mode operates in similar ways
to FASTCGI/SCGI solutions, whereby distinct processes can be dedicated
to run a WSGI application. Unlike FASTCGI/SCGI solutions however,
neither a separate process supervisor or WSGI adapter is needed when
implementing the WSGI application and everything is handled
automatically by mod_wsgi.
Because the WSGI applications in
daemon mode are being run in their own processes, the impact on the
normal Apache child processes used to serve up static files and host
applications using Apache modules for PHP, Perl or some other language
is much reduced. Daemon processes may if required also be run as a
distinct user ensuring that WSGI applications cannot interfere with each
other or access information they shouldn't be able to.
Server Performance¶
The
mod_wsgi module is written in C code directly against the internal
Apache and Python application programming interfaces. As such, for
hosting WSGI applications in conjunction with Apache it has a lower
memory overhead and performs better than existing WSGI adapters for
mod_python or alternative FASTCGI/SCGI/CGI or proxy based solutions.
Although
embedded mode can technically perform better, daemon mode would
generally be the safest choice to use. This is because to get the best
performance out of embedded mode you must tune the Apache MPM settings,
which in their default settings are biased towards serving of static
media and hosting of PHP applications. If the Apache MPM settings are
not set appropriately for the type of application being hosted, then
worse performance can be seen rather than better performance.
Thus,
unless you are adept at configuring Apache, always use daemon mode when
available. Overall, for large Python web applications you wouldn't
normally expect to see any significant difference between daemon mode
and embedded mode, as the bottlenecks are going to be in the Python web
application or any database access.
Supported Applications¶
As
mod_wsgi supports the WSGI interface specification, any Python web
framework or application which is compatible with the WSGI interface
specification should be able to be hosted on top of mod_wsgi.
Major
Python web frameworks and toolkits which are known to work include
CherryPy, Django, Pylons, TurboGears, web.py, Werkzeug and Zope. Major
Python web applications which are known to work include MoinMoin,
PyBlosxom and Trac.
System Requirements¶
The
mod_wsgi package can be compiled for and used with either Apache 1.3,
2.0 or 2.2 on UNIX systems (including Linux), as well as Windows. Either
the single threaded 'prefork' or multithreaded 'worker' Apache MPMs can
be used when running on UNIX.
Daemon mode of mod_wsgi will
however only be available on Apache 2.0 or 2.2 running on UNIX, and only
when the Apache runtime library underlying Apache has been compiled
with support for threading.
Python 2.X is required with a minimum
of Python 2.3. The Python installation being used must have been
compiled with support for threading.
The WSGI specification
currently only supports Python 2.X, so Python 3.X is not officially
supported. There is experimental support in mod_wsgi for Python 3.X
based on guesses as to what the WSGI specification may look like for
Python 3.X, however there are absolutely no guarantees that how it is
implemented will in any way match any final WSGI specification for
Python 3.X. If you still wish to experiment with Python 3.X, you will
need to use Python 3.1 or later.
Getting Started
The most up to date and recommended version of mod_wsgi is 3.3.
Ensure that you first read the documentation covering installation and configuration. Additional guidelines
are also provided for developers working with applications on top of
mod_wsgi so as to get the most out of mod_wsgi, but also to assist in
debugging problems or issues that arise with your application.
If
you don't understand a problem you are having with your application, or
believe you have found a problem with mod_wsgi, raise the issue on the mod_wsgi user group. Make sure you read the guide on where to get help first though.
Contributing¶
Developing software as Open Source is more often than not a thankless task. If you are using mod_wsgi, please consider making a donation. By giving a donation you help to ensure that mod_wsgi will continue to be developed and the documentation further improved.
Also
please note that contrary to what is being reported in some forums,
this project is in no way affiliated with Google or funded by Google (or
any other company) in any way. The only connection with Google is that
the project source code and documentation is hosted on the free and
public Google code hosting site. All development on this project is done
at my own cost in personal time.
Enjoy.
Graham Dumpleton
