See these 0.14.x to 0.15.0 upgrade instructions to bring your existing apps up to speed.

• Enhancements
  • [Socket] Introduce Phoenix.Socket behaviour that allows socket authentication, termination, and default channel socket assigns
  • [PubSub] Use ETS dispatch table for increased broadcast performance
  • [Channel] Use event intercept for increased broadcast performance
• Backward incompatible changes
  • [Router] channel routes are now defined on a socket handler module instead of the Router
  • [Router] socket mounts have been moved from the Router to the Endpoint
  • [Channel] handle_out callbacks now require explicit event intercept for callback to be invoked, with Phoenix.Channel.intercept/1
  • [Transports] WebSocket and LongPoll transport configuration has been moved from mix config to the UserSocket
• JavaScript client backwards incompatible changes
  • Phoenix.LongPoller has been renamed to Phoenix.LongPoll
  • A new client version is required to accommodate server changes