Need to somehow cache the +countrymirrors-archive page

[Guilherme Salgado]

Our existing +countrymirrors-archive page is dynamically generated every time it's accessed. That's not acceptable because once Ubuntu's apt starts using it by default, we'll have _LOTS_ of hits every second, probably DoSing LP.

Independently of how we're going to store/cache the list of mirrors for each country, we can be sure that apt will have to first issue a request to launchpad so that we can determine the country the user is, using geoip.

After that is done, there may be a few different ways to feed the list of mirrors to apt. Here are a couple of them:

1) Get a simple (text-only) list containing only the mirror URLs for a given country from the librarian and feed that data to apt. This file would be stored after each probe run and we'd use a separate table to keep the country/mirror-list mapping.

2) Point apt to a URL of the form http://foo.bar/apt-mirror-lists/<country-code> and use apache to serve these files. These will also be generated after a probe run but instead will be stored as a directory structure on disk. (This is problematic because APT doesn't follow redirects)