I'll just put this here: Anycast doesn't _necessarily_ break CDNs in the way this thread has been implying. Ideally you've got some sort of loose unicast rpf in place for your DNS nodes, and have them receive DNS queries on the anycast address, and send outbound queries out of a local interface so that the NS you're querying knows where you're located... but this is getting a bit far afield of GitHub's new features in any case. PM me if you want to here me blather about DNS and CDNs more. And cross your fingers that edns0-subnet gets implemented sometime soon.
