Yesterday, plone.org was moved on another server. It was an horrible day for our people here that didn't have a local cache of eggs to build their instances. So plone.org was acting like a Single Point Of Failure(SPOF) for some packages.
A few developers, that are under windows, were even having permission denied errors on their buildout because when a package is badly downloaded is not correctly crushed before a new attempt (I need to add a ticket about this in setuptools tracker I guess).
Anyway, we decided to create a mirror here, (I am buiding it at http://release.ingeniweb.com/ this morning hopefully) to avoid such problems.
This makes me think that zc.buildout should introduce a high-level mirror mechanism in the find-links variable, that would let someone explicitely provide a list of mirror. It could look like this:
find-links = http://pypi.python.org/simple | http://release.ingeniweb.com/pypi-mirror http://dist.plone.org | http://release.ingeniweb.com/plone-dist-mirror
It could be used to switch the find-links values sent to setuptools when the primary url is down by attempting a simple call with a timeout.