Heroku: Up and Running

Chapter 8. Buildpacks

Buildpacks provide the magic and flexibility that make running your apps on Heroku so easy. When you push your code, the buildpack is the component that is responsible for setting up your environment so that your application can run. The buildpack can install dependencies, customize software, manipulate assets, and do anything else required to run your application. Heroku didn’t always have buildpacks; they’re a new component that came with the Cedar stack.

To better understand why the buildpack system is so useful, let’s take a look at a time before buildpacks. Let’s take a look at the original Aspen stack.

Before Buildpacks

When Heroku first launched, its platform ran a stack called Aspen. The Aspen stack only ran Ruby code—version 1.8.6 to be exact. It had a read-only filesystem (no writes allowed). It had almost every publicly available Ruby dependency, known as gems, pre-installed, and it only supported Ruby on Rails applications.

Developers quickly fell in love with the Heroku workflow provided by Aspen and wanted to start using the platform for other things. The Ruby community saw Rack-based applications grow in popularity, especially Sinatra, and there was also an explosion in the number of community-built libraries being released. If you were a Ruby developer during this time you could be sure to find an acts_as library for whatever you wanted. While that was good for the community, keeping a copy of every gem on Aspen wasn’t maintainable or sane, especially ...