Heroku Preboot is a feature on Heroku that allows for faster deploy times. When you promote your staging app to production, Preboot simply switches the production server to point at the staging app's container. This means it can deploy much faster since it doesn't have to rebuild anything.

However, this means that if you use the Define Plugin to provide the rails environment to your client code as a variable, that variable will erroneously still have a value of Staging instead of Production. Providing Rails.env (which is accurate even in Preboot) in the default Rails context would be a nice enhancement.