RubyGems provides the ability of a domain to direct clients to a separate host that is used to fetch gems and make API calls against. This mechanism is implemented via DNS, specificly a SRV record _rubygems._tcp under the original requested domain. For example, this is the one that users who use rubygems.org see: > dig _rubygems._tcp.rubygems.org SRV ;; ANSWER SECTION: _rubygems._tcp.rubygems.org.