A minimal rack application, capable of being cloned from gist and deployed directly to heroku.

Rack is a fairly well known piece of the Ruby ecosystem nowadays, and is responsible for definining an interface between an HTTP request and your Ruby web app. It’s a remarkably simple interface, which can be demonstrated in a single line:

This shows the important parts of a Rackup file – you run a rack application. A rack application is a ruby object that responds to a single method ‘call’. This method takes a single argument of the environment for the request (including all the information like the header, the url, query params, etc). The call method must return an array with 3 elements – the status code, a hash of headers, and an array of body strings.

The full project (which includes a Gemfile and Procfile for heroku) is: