[irq]: techie interrupted

Every large website has this problem. A while ago Google proposed an extension to the DNS protocol to include part of the user’s IP address in the DNS lookup packet. Having a general idea of the ultimate user’s address would allow DNS load balancers to give out more intelligent answers. But convincing the whole world to adopt your protocol is hard. Fortunately, there is a cheap and cheerful way to do almost the same thing.

Remember that unique hostname, xyzzy? That can also be thought of as a unique ID for a Doppler measurement. Doppler actually results in two server-side logs. The first is the one we’ve been talking about, which contains the measurement ID, user IP, data center, and various measurements. The other comes from our DNS server. Normally, people don’t log DNS traffic but it’s easy enough to do. This second log contains the experiment’s ID paired with the resolver’s IP address.

If you were to join those logs together on the ID, then roll up by data center and resolver IP, you get a direct measurement of Internet latency between your users and your data centers, but indexed by resolver. And that’s what we’re building right now: an alternate map of the world based not on geographic distance, but on pure network latency.