Having run into compatibility issues between Passenger and RJB and between Mongrel and Rails 2.3.8 I’ve been looking at Thin.
Slicehost has a couple of good articles on setting up a Thin cluster with Apache on Ubuntu.
In summary:
gem install thin
thin install
/usr/sbin/update-rc.d -f thin defaults
thin –h # help
thin -C /etc/thin/${appenv}.yml -c ${apphome} -s 3 -e production config
su – ${appenv}bat ; thin -C /etc/thin/${appenv}.yml start