So Wix uses MySQL to resolve site routes internally? Is this the best way to do it? Would it be possible to use internal domain names and rely on DNS to resolve everything?
Re: nosql, I'm coming at that with really positive experiences in Cassandra but I can't imagine what kind of DNS system it would be a good fit for. The ability to tune CAP to fit DNS may be useful but in general I think of Cassandra as the solution you think about when your 2 node vertically scaled monster can't keep up.
You get free caching which is tolerant to partitions, but you'd get that with either solution since it's largely the forwarding dns servers which make that happen and the difference here is constrained to the authorative resolving dns servers.
For companies other than Wix I don't know what is used to handle it on the back end but I imagine it's either some specialized piece of hardware than can handle an insane load or some commodity hardware / cloud service & in-house software like here.
At the end of the day, and I'm sure I'm missing some edge cases, I think it's basically a service that provides a mapping of domain.com/user-resource-or-website to the location of their resources with no lag time when changes are made.