Rack & Roll!

As we mentioned earlier, Cuba is built on top of Rack ... but what is Rack?

Rack deals with HTTP requests. It provides a minimal interface between web servers supporting Ruby and Ruby frameworks. Without Rack, Cuba would have to implement its own handler for each web server.

You didn't notice yet but we already used Rack. We used rackup, one of the tools that comes with Rack, to run our "Hello Cuba!" application.

To use rackup, you need to supply a config file (by convention it uses the .ru extension). This file connects the Rack interface with your application through the run method. This method receives an object that returns a Rack response. In our case, that object is Cuba:

run(Cuba)

rackup also figures out which server you have available. When we executed rackup config.ru, it fired up WEBrick, a web server built into Ruby by default.

$ rackup config.ru
[2014-05-06 23:37:23] INFO  WEBrick 1.3.1
...

To read more about Rack, visit their home page.