Safe to modify settings.SITE_ID from middleware in Django?

Question

I have modified the multihost.py middleware I found at http://effbot.org/zone/django-multihost.htm to set the settings.SITE_ID dynamically, but have some concerns that I may have just left the reservation.

Most examples I have found for multiple domain hosting have been setup with multiple settings.py files hardcoded to their respective SITE_IDs.

Have I created a fix with a fatal flaw here? Will changing this value dynamically bite me on the a**.

from django.conf import settings
from django.contrib.sites.models import Site

class MultiHostMiddleware:

    def process_request(self, request):
        try:
            host_raw = request.META["HTTP_HOST"]
            colon = host_raw.find(':')
            if colon > -1:
                host = host_raw[0:colon]
            else:
                host = host_raw

            s = Site.objects.get(domain=host)
            if s:
                settings.SITE_ID = s.id

        except KeyError:
            pass # use default urlconf (settings.ROOT_URLCONF)

For the curious this is up and running so far, but has not stood up to actual traffic.

Answer 1

The short, official answer is you're not supposed to do this, though the docs don't really explain why not.

If you're using a threaded server, I'd be concerned about a race condition. This should be quite simple to test; just put a call to sleep() in one view, then return an HttpResponse with the name of the current site. While the first view is sleeping, hit a different view on a different domain.

If you use prefork, I don't imagine that this would cause any problems. I've used this approach with matplotlib, since it's easiest to set graph properties by changing global configuration with matplotlib.rcParams.update(). I use prefork fcgi, so I can safely assume that each request has the whole process to itself (folks, please correct me if I'm wrong).

Edit: I think you can do what you want using RequestSite by disabling the sites application. James Bennett's django-registration, for example, instantiates a RequestSite object in that case, which extracts the hostname from the request object.