How to Run a basic Rack App on Cloud9

Cloud9 is an awesome online development environment that supports Node.js, Rails, and Sinatra. It also supports basic Rack apps. The preview button on Cloud9 is good for simple html files and node apps, but what if you have a very simple Rack app? I have one just to serve some static files. Here’s what you need to get it runing:

1. open a terminal window
2. type rackup -p $PORT -o $IP

$PORT and $IP are environment variables that are already set in your Cloud9 bash environment.