In config/{dev,prod}.exs:

config :the_app, TheApp.Endpoint,
  http: [ip: {127,0,0,1}, port: 1234],

IP address must be in tuple format {127,0,0,1}.

alias wanip='dig +short myip.opendns.com @resolver1.opendns.com'
alias ipaddr='wanip && ipconfig getifaddr en1'