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One of the things I hear from time to time is how smaller Internet facing service deployments, with just a few instances, cannot really benefit from anycast. Particularly in the active-active data center use case, where customers can connect to one data center or another, the cost of advertising the service as an anycast, and the resulting requirement to keep the backend databases tightly synchronized, is often played as a eating a lot of complexity for the simplicity of having a single address in the DNS system, and hence not losing customer interaction time while the DNS records are timing out so the customer can reconnect to the service.
There is, in fact, some interesting recent research in this area. The research is directed at the DNS root servers themselves, probably because they are publicly accessible, and a well known system that has relied on anycast for many years (so the operators of the root DNS servers are probably well versed in the ways of anycast). One interesting chart from the post over at APNIC’s blog is—

The C root has 8 servers, while the L root has around 144 (according to the article pointed to above). Why is it Continue reading