Does heroku use rvm or rbenv?
I'm reading https://github.com/heroku/stack-images/blob/master/bin/cedar-14.sh
and there's no mention of rvm. Yet I know for a fact then when you do
git push heroku master
the apropriate ruby magically manifests itself in the remote heroku lxc container.
They have custom scripts for downloading and installing ruby. Or at least it looks like that from those scripts:
https://github.com/heroku/heroku-buildpack-ruby/blob/master/bin/support/download_ruby https://github.com/heroku/heroku-buildpack-ruby/blob/master/lib/language_pack/installers/heroku_ruby_installer.rb
