Heroku provides the following instructions for those starting from scratch with JRuby:
All you need to do is specify the version of Ruby you want to run, the engine, and the engine version in your Gemfile:
ruby '1.9.3', engine: 'jruby', engine_version: '1.7.1'
You'll need to run bundle install with JRuby locally, then commit the results and push to Heroku:
$ git add . $ git commit -m "trying JRuby on Heroku" $ git push heroku master Counting objects: 692, done. Delta compression using up to 4 threads. Compressing objects: 100% (662/662), done. Writing objects: 100% (692/692), 141.01 KiB, done. Total 692 (delta 379), reused 0 (delta 0) -----> Heroku receiving push -----> Ruby/Rails app detected -----> Using Ruby version: ruby-1.9.3-jruby-1.7.1 -----> Installing JVM: openjdk7-latest -----> Installing dependencies using Bundler version 1.2.1 # ...
Heroku also provides instructions for moving existing rails apps to JRuby.
JRuby support is live now, so you can get git-pushing immediately if you like. And if you do, let us know what you think of the experience.