Yes: Gmail (IMAP and SMTP), Google Chat (XMPP), etc. Try it out...do the DNS lookups yourself from different places.
So, it's only Google doing it?
FTP? Smtp? Distributed file shares? SQL server mirrors? NNTP? Ntp? I could probably list a dozen more.
Yes, that's a list of common internet protocols. I do not know of any example of anyone actually using geolocated DNS to CDN them. Do you have a concrete example?
Because it works, and there is more out there than just HTTP. This same approach will work for any protocol that uses DNS to resolve domain names.
Except that this is only used for HTTP. I do not know of any non-HTTP examples.
And here we have the real reason why this is being promoted:
3. And IMO most importantly, this removes the server selection choice from being under the sole control of the CDN provider. If this stuff is logic'd through the main HTTP page of the website, the CDN must expose its server selection strategy to the client, which is likely proprietary business knowledge.
It breaks DNS. It certainly breaks my local DNS installation, for starters. It also means that *everyone* must use this DNS hack because service will be degraded unless you do.
Messing with DNS is doing it the Wrong Way. All of these CDN services are based on HTTP. When you're using them, that's an HTTP server you're talking to. It's perfectly capable of geolocating you by IP, and it can either hand you back links to a local CDN, or redirect you to another server.
Why the hell must we mess with DNS to do this? This is a solution which only works if you use Google DNS, OpenDNS, or sometimes if you use your local ISP's DNS. What if you're just running bind for you local net vs the root servers? Bzzt. Doesn't work.
The most insane thing about this is it's Google we're talking about here. They damn well know how to implement this entirely in their servers without resorting to DNS hacks. Why are they promoting this net-neutrality breaking, layering violating botch? We need less people to use this, not more.
To write good code is a worthy challenge, and a source of civilized delight. -- stolen and paraphrased from William Safire