The concurrency tuning explained in that article has got nothing to do with reverse proxying. You don't need multiple processes either: the article says that you can use multithreading, and especially in the case of I/O-bound apps, that's enough. If you want to leverage multiple CPU cores however, that's a different story, but it depends on your Ruby implementation. If you use JRuby or Rubinius then threads are enough. But that is still unrelated to the question of whether to reverse proxy or not.