The Twelve Factors App is a methodology that a web application should follow to be able to easily deploy and scale on today’s SAAS platform like Heroku. This methodolgy is announced by the Heroku Founder Adam Wiggins. The content is the based on their experience of deploying millions of applications.
When I first saw this declaration, I just feel that this might be extract from rails and herokus best practices, but actually this declaration is more then practices but a methodology to improve the maintainbility and scalability of web application. so I like to share Heroku engineer’s slide about 12 factors app: