Apache with mod_python currently is the preferred setup for using Django
on a production server.
mod_python is similar to (and inspired by) mod_perl : It embeds Python within
Apache and loads Python code into memory when the server starts. Code stays in
memory throughout the life of an Apache process, which leads to significant
performance gains over other server arrangements.
Django requires Apache 2.x and mod_python 3.x, and you should use Apache’s
prefork MPM, as opposed to the worker MPM.
You may also be interested in How to use Django with FastCGI, SCGI or AJP (which also covers SCGI and AJP).
Basic configuration¶
To configure Django with mod_python, first make sure you have Apache installed,
with the mod_python module activated.
Then edit your httpd.conf file and add the following:
<Location "/mysite/">
SetHandler python-program
PythonHandler django.core.handlers.modpython
SetEnv DJANGO_SETTINGS_MODULE mysite.settings
PythonOption django.root /mysite
PythonDebug On
</Location>
...and replace mysite.settings with the Python import path to your Django
project's settings file.
This tells Apache: "Use mod_python for any URL at or under '/mysite/', using the
Django mod_python handler." It passes the value of DJANGO_SETTINGS_MODULE so mod_python knows which settings to use.
New in Django 1.0: The PythonOption django.root ... is new in this version.
Because mod_python does not know we are
serving this site from underneath the /mysite/ prefix, this value needs to
be passed through to the mod_python handler in Django, via the PythonOption
django.root ... line. The value set on that line (the last item) should
match the string given in the <Location ...> directive. The effect of this
is that Django will automatically strip the /mysite string from the front
of any URLs before matching them against your URLConf patterns. If you
later move your site to live under /mysite2, you will not have to change
anything except the django.root option in the config file.
When using django.root you should make sure that what's left, after the
prefix has been removed, begins with a slash. Your URLConf patterns that are
expecting an initial slash will then work correctly. In the above example,
since we want to send things like /mysite/admin/ to /admin/, we need
to remove the string /mysite from the beginning, so that is the
django.root value. It would be an error to use /mysite/ (with a
trailing slash) in this case.
Note that we're using the <Location> directive, not the <Directory>
directive. The latter is used for pointing at places on your filesystem,
whereas <Location> points at places in the URL structure of a Web site.
<Directory> would be meaningless here.
Also, if your Django project is not on the default PYTHONPATH for your
computer, you'll have to tell mod_python where your project can be found:
<Location "/mysite/">
SetHandler python-program
PythonHandler django.core.handlers.modpython
SetEnv DJANGO_SETTINGS_MODULE mysite.settings
PythonOption django.root /mysite
PythonDebug On
PythonPath "['/path/to/project'] + sys.path"
</Location>
The value you use for PythonPath should include the parent directories of
all the modules you are going to import in your application. It should also
include the parent directory of the DJANGO_SETTINGS_MODULE location. This is exactly the same situation as
setting the Python path for interactive usage. Whenever you try to import
something, Python will run through all the directories in sys.path in turn,
from first to last, and try to import from each directory until one succeeds.
An example might make this clearer. Suppose you have some applications under
/usr/local/django-apps/ (for example, /usr/local/django-apps/weblog/ and
so forth), your settings file is at /var/www/mysite/settings.py and you have
specified DJANGO_SETTINGS_MODULE as in the above
example. In this case, you would need to write your PythonPath directive
as:
PythonPath "['/usr/local/django-apps/', '/var/www'] + sys.path"
With this path, import weblog and import mysite.settings will both
work. If you had import blogroll in your code somewhere and blogroll
lived under the weblog/ directory, you would also need to add
/usr/local/django-apps/weblog/ to your PythonPath. Remember: the
parent directories of anything you import directly must be on the Python
path.
Note
If you're using Windows, we still recommended that you use forward
slashes in the pathnames, even though Windows normally uses the backslash
character as its native separator. Apache knows how to convert from the
forward slash format to the native format, so this approach is portable and
easier to read. (It avoids tricky problems with having to double-escape
backslashes.)
This is valid even on a Windows system:
PythonPath "['c:/path/to/project'] + sys.path"
You can also add directives such as PythonAutoReload Off for performance.
See the mod_python documentation for a full list of options.
Note that you should set PythonDebug Off on a production server. If you
leave PythonDebug On, your users would see ugly (and revealing) Python
tracebacks if something goes wrong within mod_python.
Restart Apache, and any request to /mysite/ or below will be served by
Django. Note that Django's URLconfs won't trim the "/mysite/" -- they get passed
the full URL.
When deploying Django sites on mod_python, you'll need to restart Apache each
time you make changes to your Python code.
Multiple Django installations on the same Apache¶
It's entirely possible to run multiple Django installations on the same Apache
instance. Just use VirtualHost for that, like so:
NameVirtualHost *
<VirtualHost *>
ServerName www.example.com
# ...
SetEnv DJANGO_SETTINGS_MODULE mysite.settings
</VirtualHost>
<VirtualHost *>
ServerName www2.example.com
# ...
SetEnv DJANGO_SETTINGS_MODULE mysite.other_settings
</VirtualHost>
If you need to put two Django installations within the same VirtualHost
(or in different VirtualHost blocks that share the same server name),
you'll need to take a special precaution to ensure mod_python's cache doesn't
mess things up. Use the PythonInterpreter directive to give different
<Location> directives separate interpreters:
<VirtualHost *>
ServerName www.example.com
# ...
<Location "/something">
SetEnv DJANGO_SETTINGS_MODULE mysite.settings
PythonInterpreter mysite
</Location>
<Location "/otherthing">
SetEnv DJANGO_SETTINGS_MODULE mysite.other_settings
PythonInterpreter othersite
</Location>
</VirtualHost>
The values of PythonInterpreter don't really matter, as long as they're
different between the two Location blocks.
Running a development server with mod_python¶
If you use mod_python for your development server, you can avoid the hassle of
having to restart the server each time you make code changes. Just set
MaxRequestsPerChild 1 in your httpd.conf file to force Apache to reload
everything for each request. But don't do that on a production server, or we'll
revoke your Django privileges.
If you're the type of programmer who debugs using scattered print
statements, note that print statements have no effect in mod_python; they
don't appear in the Apache log, as one might expect. If you have the need to
print debugging information in a mod_python setup, either do this:
assert False, the_value_i_want_to_see
Or add the debugging information to the template of your page.
Serving media files¶
Django doesn't serve media files itself; it leaves that job to whichever Web
server you choose.
We recommend using a separate Web server -- i.e., one that's not also running
Django -- for serving media. Here are some good choices:
If, however, you have no option but to serve media files on the same Apache
VirtualHost as Django, here's how you can turn off mod_python for a
particular part of the site:
<Location "/media">
SetHandler None
</Location>
Just change Location to the root URL of your media files. You can also use
<LocationMatch> to match a regular expression.
This example sets up Django at the site root but explicitly disables Django for
the media subdirectory and any URL that ends with .jpg, .gif or
.png:
<Location "/">
SetHandler python-program
PythonHandler django.core.handlers.modpython
SetEnv DJANGO_SETTINGS_MODULE mysite.settings
</Location>
<Location "/media">
SetHandler None
</Location>
<LocationMatch "".(jpg|gif|png)$">
SetHandler None
</LocationMatch>
Serving the admin files¶
Note that the Django development server automagically serves admin media files,
but this is not the case when you use any other server arrangement. You're
responsible for setting up Apache, or whichever media server you're using, to
serve the admin files.
The admin files live in (django/contrib/admin/media) of the Django
distribution.
Here are two recommended approaches:
- Create a symbolic link to the admin media files from within your
document root. This way, all of your Django-related files -- code and
templates -- stay in one place, and you'll still be able to svn
update your code to get the latest admin templates, if they change.
- Or, copy the admin media files so that they live within your Apache
document root.
Using "eggs" with mod_python¶
If you installed Django from a Python egg or are using eggs in your Django
project, some extra configuration is required. Create an extra file in your
project (or somewhere else) that contains something like the following:
import os
os.environ['PYTHON_EGG_CACHE'] = '/some/directory'
Here, /some/directory is a directory that the Apache webserver process can
write to. It will be used as the location for any unpacking of code the eggs
need to do.
Then you have to tell mod_python to import this file before doing anything
else. This is done using the PythonImport directive to mod_python. You need
to ensure that you have specified the PythonInterpreter directive to
mod_python as described above (you need to do this even if you aren't
serving multiple installations in this case). Then add the PythonImport
line in the main server configuration (i.e., outside the Location or
VirtualHost sections). For example:
PythonInterpreter my_django
PythonImport /path/to/my/project/file.py my_django
Note that you can use an absolute path here (or a normal dotted import path),
as described in the mod_python manual. We use an absolute path in the
above example because if any Python path modifications are required to access
your project, they will not have been done at the time the PythonImport
line is processed.
Error handling¶
When you use Apache/mod_python, errors will be caught by Django -- in other
words, they won't propagate to the Apache level and won't appear in the Apache
error_log.
The exception for this is if something is really wonky in your Django setup. In
that case, you'll see an "Internal Server Error" page in your browser and the
full Python traceback in your Apache error_log file. The error_log
traceback is spread over multiple lines. (Yes, this is ugly and rather hard to
read, but it's how mod_python does things.)
If you get a segmentation fault¶
If Apache causes a segmentation fault, there are two probable causes, neither
of which has to do with Django itself.
- It may be because your Python code is importing the "pyexpat" module,
which may conflict with the version embedded in Apache. For full
information, see Expat Causing Apache Crash.
- It may be because you're running mod_python and mod_php in the same
Apache instance, with MySQL as your database backend. In some cases,
this causes a known mod_python issue due to version conflicts in PHP and
the Python MySQL backend. There's full information in the
mod_python FAQ entry.
If you continue to have problems setting up mod_python, a good thing to do is
get a barebones mod_python site working, without the Django framework. This is
an easy way to isolate mod_python-specific problems. Getting mod_python Working
details this procedure.
The next step should be to edit your test code and add an import of any
Django-specific code you're using -- your views, your models, your URLconf,
your RSS configuration, etc. Put these imports in your test handler function
and access your test URL in a browser. If this causes a crash, you've confirmed
it's the importing of Django code that causes the problem. Gradually reduce the
set of imports until it stops crashing, so as to find the specific module that
causes the problem. Drop down further into modules and look into their imports,
as necessary.