A stack is a complete deployment environment including the base operating system, the language runtime and associated libraries. As a result, different stacks support different runtime environments.

Stack summary

The current default stack is bamboo-mri-1.9.2. You may target a different stack when creating an app or change stacks on an existing app via a stack migration.

You can see what stack your app is on, and all available stacks, using the heroku CLI:

$ heroku stack
  aspen-mri-1.8.6
  bamboo-ree-1.8.7
* bamboo-mri-1.9.2
  cedar (beta)

Here, the app is running on Badious Bamboo, using MRI 1.9.2. The Argent Aspen stack and the Celadon Cedar are also available to this app.

Using a specific stack

You may specify a non-default stack during app creation with the --stack (or -s) flag:

$ heroku create --stack cedar
Creating glowing-mist-330... done, stack is cedar
http://glowing-mist-330.heroku.com/ | git@heroku.com:glowing-mist-330.git

This app is now automatically setup to use the Cedar stack, which supports several languages and frameworks.

Migrating to Bamboo

Migrating to Bamboo is a simple and automated process. Detailed instructions can be found on the “About Bamboo” page.

Migrating to Cedar

Migrating from Bamboo to Cedar allows an application to take advantage of a much more flexible and powerful stack. Because the significant architectural differences, migrating to Cedar is a largely manual process.

You can find instructions for migrating to Cedar here.