RVM + Monit

monit.rc

# thin
# assuming there's an appropriate .rvmrc in /path_to_rails_app/current

cd rails_app/current
gem install thin
rvm wrapper your_ruby@your_gemset your_app_name thin

# now we can use your_app_name_thin in Monit scripts

# /etc/monit.d
# repeat for each port identified in config/thin.yml
# in this example port = 8000
#
# username and password is that of the account your_app runs in

check process thin-8000 with pidfile /path_to_rails_app/current/tmp/pids/thin.8000.pid
  start program = "/path_to_your_app_name_thin -u user_name -g group -C /path_to_rails_app/current/config/thin.yml start --only 8000"
  stop program = "/path_to_your_app_name_thin -u user_name -g group -C /path_to_rails_app/current/config/thin.yml stop --only 8000"

  if totalmem is greater than 120.0 MB for 5 cycles then restart  # eating up memory?
  if cpu is greater than 50% for 2 cycles then alert              # send an email to admin
  if cpu is greater than 80% for 3 cycles then restart            # hung process?
  if loadavg(5min) greater than 10 for 8 cycles then restart      # bad, bad, bad
  if 3 restarts within 5 cycles then timeout                      # something is wrong, call the sys-admin

group thin

# assuming Capistrano deployment, this in deploy.rb

set :thin_config, "#{deploy_to}/current/config/thin.yml"

namespace :deploy do
  task :start do
    run "your_app_name_thin start -u user_name -g password -C #{thin_config}"
  end

  task :stop do
    run "your_app_name_thin stop -u user_name -g password -C #{thin_config}"
  end

  task :restart, :roles => :app, :except => { :no_release => true } do
    stop
    # to let monit start these, remove start, but I prefer to be explicit
    # and not have to wait for monit to detect
    start
  end
end