How can I monitor an ActionController::Metal with NewRelic?

Question

I have a Rails 3 application of which some controllers are normal rails controllers and some are implemented using ActionController::Metal. By default, NewRelic monitors the normal rails controllers but not the NewRelic ones.

It seems that NewRelic supports Rack applications, but the code examples given are either when there is a specific piece of middleware you want to monitor, or when you have a MetalApp you are defining. Neither seems to work with ActionController::Metal.

So, how do I add NewRelic monitoring to my metal controllers?

Answer 1

New Relic support suggested:

class SteelController < ActionController::Metal     
  include ActionController::Rendering                 

  def show
    render :text => { :data => 1 }.to_json           
  end                     
  include NewRelic::Agent::Instrumentation::ControllerInstrumentation     
  add_transaction_tracer :show     

end 

which seems to work.