CODEWITHSUNDEEP
pythondjangoapache
Gav
Gav

Reputation: 237

Problems hosting multiple django sites (settings cross over)

I have recently set up a web server, which currently hosts a couple of static page websites, and two django projects.

the two django projects are 'abc' and 'xyz' and are in separate directories respectively, in the home folder. Each have their own wsgi script which points to their respective settings.py file.

Recently though, I have been noticing a few 500 errors on 'xyz'. Usually a refresh will correct the problem, but this isn't acceptable, so I checked the apache error.log, and noticed that sometimes when I hit 'xyz' there is an exception raised about cannot find abc.settings in the xyz project. Somehow these two projects are crossing over and interfering with each other. I have not worked on abc enough yet to know if the problem is the same the other way around. Below is my exception.

[Sun Jul 08 13:30:34 2012] [error] Traceback (most recent call last):
[Sun Jul 08 13:30:34 2012] [error] File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/wsgi.py", line 219, in __call__
[Sun Jul 08 13:30:34 2012] [error]    self.load_middleware()
[Sun Jul 08 13:30:34 2012] [error]    File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py", line 39, in load_middleware
[Sun Jul 08 13:30:34 2012] [error]      for middleware_path in settings.MIDDLEWARE_CLASSES:
[Sun Jul 08 13:30:34 2012] [error]    File "/usr/local/lib/python2.7/dist-packages/django/utils/functional.py", line 184, in inner
[Sun Jul 08 13:30:34 2012] [error]      self._setup()
[Sun Jul 08 13:30:34 2012] [error]    File "/usr/local/lib/python2.7/dist-packages/django/conf/__init__.py", line 42, in _setup
[Sun Jul 08 13:30:34 2012] [error]      self._wrapped = Settings(settings_module)
[Sun Jul 08 13:30:34 2012] [error]    File "/usr/local/lib/python2.7/dist-packages/django/conf/__init__.py", line 95, in __init__
[Sun Jul 08 13:30:34 2012] [error]      raise ImportError("Could not import settings '%s' (Is it on sys.path?): %s" % (self.SETTINGS_MODULE, e))
[Sun Jul 08 13:30:34 2012] [error]  ImportError: Could not import settings 'abc.settings' (Is it on sys.path?): No module named scalamoosh.settings

Any help/advice would be greatly appreciated. Cheers

Upvotes: 2

Views: 1572

Answers (4)

Graham Dumpleton
Graham Dumpleton

Reputation: 58563

The default configuration for mod_wsgi has the two Django sites running in separate sub interpreters of the same process. Unfortunately Django changed their generated wsgi.py in 1.4 and the new file breaks with this default behaviour of mod_wsgi. To fix the issue if using Django 1.4, go into the wsgi.py file and change:

os.environ.setdefault("DJANGO_SETTINGS_MODULE", "mysite.settings")

to:

os.environ["DJANGO_SETTINGS_MODULE"] = "mysite.settings"

That is, don't use os.environ.setdefault() because it will not do anything when variable has already been set by other Django site in the other sub interpreter due to the way environment variables leak between sub interpreters.

Better still, use mod_wsgi daemon mode and create distinct daemon process groups for each site and delegate them to run in different sets of processes. This can solve a similar issue with older Django versions where a not quite correct Apache configuration for VirtualHosts has been used.

Upvotes: 3

Joe Day
Joe Day

Reputation: 7274

The issue you're running in to is that while mod_wsgi gives each Django app its own python interpreter, they still share the same OS environment which is where Django stores the name of the setting module. The work-around I found was to change the name of the enviroment variable that Django looks for the settings module in before creating the WSGI application object.

My slightly modified wsgi.py looks something like this:

import os

# change the env variable where django looks for the settings module
import django.conf
django.conf.ENVIRONMENT_VARIABLE = "DJANGO_SECOND_SETTINGS_MODULE"

os.environ.setdefault("DJANGO_SECOND_SETTINGS_MODULE", "second.settings")

# This application object is used by any WSGI server configured to use this
# file. This includes Django's development server, if the WSGI_APPLICATION
# setting points here.
from django.core.wsgi import get_wsgi_application
application = get_wsgi_application()

Upvotes: 5

Gerard Yin
Gerard Yin

Reputation: 1313

Are you using memcached for the cache, or any other caching method where the two instances could write in the same cache file? That could explain why the two environments get mixed up. In that case, simply add a KEY_PREFIX variables in your settings' CACHES dictionary.

CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
        'LOCATION': '127.0.0.1:11211',
        'KEY_PREFIX': 'scalamoosh'
    }
}

Upvotes: 0

Herman Schaaf
Herman Schaaf

Reputation: 48445

It doesn't look like you are using separate virtual environments for your two projects at the moment, and if not, I would highly recommend doing so and seeing if the problem persists thereafter. You can still use the same Apache instance, but run two separate instances of Django (and all the other requirements of the projects, which may or may not differ). This is normally the recommended approach for any Django project.

If you don't know about virtual environments, here's a quickstart tutorial on using virtualenv and Django, and I would also recommend using the very nice Virtualenv Wrapper by Doug Hellman. Hope this helps!

Upvotes: 2

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