The docs for instrumenting your Sinatra app with New Relic on Heroku are either wrong or a bit sparse. Its actually very simple.
- Add the newrelic_rpm gem to either your .gems or Gemfile
- require the rpm library when in production
configure :production do require 'newrelic_rpm' end
- add the heroku new_relic addon
heroku addons:add newrelic:bronze
A full working example is here!