What is the correct way to specify the Ruby version in a Rails app, using RVM, that will be deployed on Heroku?

Question

The RVM Best Practices state that, to connect a project to a specific Ruby version, you should specify that version in the project-specific rvmrc file.

This SO answer states that, in most situations, you should use specify the Ruby version in the .ruby-version file.

Heroku says you should specify the Ruby version in Gemfile.

What is the correct way to specify a Ruby version, using RVM, if the app will be deployed on Heroku?

Answer 1

.rvmrc is deprecated and you should use .ruby-version instead.

But Heroku does not pay attention to the .ruby-version. Heroku wants to have it in the Gemfile. So I think you should use both: .ruby-version (for you) and Gemfile (for Heroku).

Answer 2

You need to place it in the Gemfile for Heroku's sake, but if you're using a version manager, then you'll need to use something else for the sake of the version manager. I think the SO answer makes sense in that regard (i.e. the .ruby-version file).