Heroku and The Art of The 12 Factor Application. Heroku is an opinionated cloud development platform. Most of our opinions stem directly from the belief that solid SaaS architectures adhere to a simple set of 12 rules. We’ll walk through deploying a basic Rails application on Heroku, highlighting platform design decisions that are motivated by the 12 factor approach to development. By the end you’ll have a nice collection of design patterns that you can apply immediately to improve application health, accelerate development and increase the happiness of your team.