Despite its popularity WEBrick has gained some notoriety since the code is completely undocumented.
– Wikipedia’s WEBrick page

WEBrick is the little web server in the Ruby standard library, and I’ve used it several times when I’ve needed to embed a little server in a project. I noticed a couple of problems in my latest little program: it took a few seconds to start up, and always included a “TCPServer Error: Address already in use – bind(2)” warning in its startup messages.

After watching this happen a few dozen times, I found solutions to both these annoyances, and they’re here in the hope that someone else will Google their way here: just create your server object like this:

# This fixes the slow startup
Socket.do_not_reverse_lookup = true
 
# Using :BindAddress to say "bind to all interfaces" fixes the address-in-use warning
server = HTTPServer.new(:Port => my_port_number, :BindAddress => "0.0.0.0")