lazy-loading class-based-views in Django

So one of the nice things with method-based views in Django is the ability to do this sort of thing to load a view at the path frontend.views.home:

urlpatterns = patterns(

    url(r'^$', 'home', name='home'),

Unfortunately, if you’re using class-based-views, you can’t do this:

urlpatterns = patterns(

    url(r'^$', 'HomeView', name='home'),

And instead you had to resort to importing the view and calling HomeView.as_view(). Sort of annoying when you didn’t want to import all of those views.

It turns out however that overloading the code to resolve HomeView is not that difficult, and we can do it with a pretty straightforward monkeypatch. This version uses the kwargs argument of url() to pass keyword arguments to as_view().

from django.conf import urls
from django.views.generic import View

class ClassBasedViewURLPattern(urls.RegexURLPattern):
    A version of RegexURLPattern able to handle class-based-views

    Monkey-patch it in to support class-based-views

    def callback(self):
        Hook locating the view to handle class based views

        view = super(ClassBasedViewURLPattern, self).callback

        if isinstance(view, type) and issubclass(view, View):
            view = view.as_view(**self.default_args)
            self.default_args = {}

        return view

urls.RegexURLPattern = ClassBasedViewURLPattern

A libnss plugin for Docker

So we’ve been starting to use Docker at Infoxchange. A little while ago my Infoxchange colleague Ricky Cook wrote a Twisted service to resolve Docker container names into their private IP addresses.

I thought this was a pretty neat idea, although you had to do some things like return SERVFAIL to round-robin to another DNS server if it wasn’t a Docker host. However it got problematic when something like dhclient/NetworkManager was in charge of your resolv.conf.

I realised on Friday night the the Truely UNIX solution was to write an NSS plugin. This was not quite as trivial as I thought it would be. However I spent a bit of time staring at Lennart’s mdns plugin and started writing one of my own.

docker-nss should work well enough to resolve container IDs and temporary assigned names that you get from docker ps.

There’s a bit of work to do. It can’t reverse IPs back into container names yet. Nor does it return a full list of aliases for a container. Nor does it return a list of IPs for an image name. Patches welcome! It currently depends on GLib, which drags GLib into the memory space of every process on your system, however it wouldn’t be too hard to port away from it (I’m just lazy).

It has unit tests via a mocked docker client. You do have to have modified your nsswitch.conf in order to be able to run the tests. Although if this really bothers someone we could make the test suite itself a Docker container.