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...).
Gemfile gem 'em-udns', '~> 0.3.2'
install gem install em-udns -v 0.3.2