The Twelve-Factor App (opens in new tab)

For the inexperienced, it might be informative to have a list of the most common mistakes & errors.

But then, you also can see at once that this post came directly from the Dark Ages when people believed in silver bullets named “Methodology”. The post even mentions Martin Fowler's bestiary (Patterns of Enterprise Application Architecture) as an inspiration. So don't say you haven't been warned...

This document is largely an artifact from Heroku's early days with a purpose to get people to bend deploying their applications to the way Heroku wants you to deploy your applications. Some of the points are good (use environment variables) but others are blatantly in Heroku's best interests and not yours (preferring process forking on a company that charges by RAM... Hmmmm).