See these 0.15.x to 0.16.0 upgrade instructions to bring your existing apps up to speed.

• Enhancements
  • [Brunch] No longer ship with sass-brunch dependency
  • [Endpoint] Add force_ssl support
  • [Mix] Allow phoenix.gen.* tasks templates to be customized by the target application by placing copies at priv/template/phoenix.gen.*
  • [Mix] Support mix phoenix.gen.model Comment comment post_id:references:posts
  • [Mix] Add mix phoenix.gen.secret
  • [Router] Provide put_secure_browser_headers/2 and use it by default in the browser pipeline
  • [Socket] Automatically check origins on socket transports
  • [Token] Add Phoenix.Token for easy signing and verification of tokens
• Bug fixes
  • [Cowboy] Ensure we print proper URL when starting the server with both http and https
  • [Digest] Do not gzip binary files like png and jpg. Default only to known text files and make them configurable via config :phoenix, :gzippable_exts, ~w(.txt .html .js .css) and so on
• Backward incompatible changes
  • [Controller] jsonp/3 function has been removed in favor of the plug :allow_jsonp
  • [Controller] controller_template/1 has been renamed to view_template/1
  • [HTML] Use phoenix_html ~> 2.0 which includes its own phoenix_html.js version
  • [Socket] :origins transport option has been renamed to :check_origin
  • [View] render_one and render_many no longer inflect the view module from the model in favor of explicitly passing the view
• JavaScript client backwards incompatible changes
  • Socket params are now passed to socket.connect() instead of an option on the constructor.
  • Socket params are no longer merged as default params for channel params. Use connect/2 on the server to wire up default channel assigns.
  • Socket chan has been renamed to channel, for example socket.channel("some:topic")