em-udns

https://github.com/ibc/em-udns

em-udns is an async DNS resolver for EventMachine based on udns C library. Having most of the core written in C, em-udns becomes very fast. It can resolve DNS A, AAAA, PTR, MX, TXT, SRV and NAPTR records, and can handle every kind of errors (domain/record not found, request timeout, malformed response...).