From OCS Support Wiki

Introduction

This guide will help you diagnose the problem that is causing the 503 error on your site.

Ruby on Rails

If you are using a Ruby on Rails application on your website, this error means the Mongrel process is not responding. The causes of this are:

• Your Mongrel process terminated. You will need to restart it. If it does not start, please see Troubleshooting a Ruby on Rails Application.
• You do not have the application set to start on boot. If this is the case, please see Starting Your Application At Boot.

Avoiding This Error

To avoid this error with Ruby on Rails apps, please consider deploying your application with Passenger. To find out more about this, please see Deploying a Rails Application With Passenger