NewRelic RPM with ActionController::Metal

Damian Galarza — Wed, 05 Sep 2012 00:00:00 +0000

As part of our work with the QFive API for internal consumption we’ve built it out using Rails’ ActionController::Metal. We quickly realized that incoming requests to the API were not being tracked by NewRelic and looked for a way to resolve this. A quick google search will yield this documentation from New Relic which includes the following example:

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

  def show
    render :text => "Here is some text"
  end
  include ::NewRelic::Agent::Instrumentation::ControllerInstrumentation
  add_transaction_tracer :show
end

While this works, the problem remains that now you will need to add a transaction tracer for each and every controller action you add.

With this in mind I went in search of a better solution which could streamline the solution. Digging around the NewRelic RPM gem internals I was able to find the ‘magic’ behind the way New Relic integrates into requests. Within lib/new_relic/agent/instrumentation/rails3/action_controller.rb you can find the following:

DependencyDetection.defer do
  @name = :rails3_controller

  depends_on do
    defined?(::Rails) && ::Rails::VERSION::MAJOR.to_i == 3
  end

  depends_on do
    defined?(ActionController) && defined?(ActionController::Base)
  end

  executes do
    NewRelic::Agent.logger.debug 'Installing Rails 3 Controller instrumentation'
  end

  executes do
    class ActionController::Base
      include NewRelic::Agent::Instrumentation::ControllerInstrumentation
      include NewRelic::Agent::Instrumentation::Rails3::ActionController
    end
  end
end

Which handles including the various instrumentation tools for ActionController. With this in mind we can follow the same logic in our API BaseController:

require 'new_relic/agent/instrumentation/controller_instrumentation'
require 'new_relic/agent/instrumentation/rails3/action_controller'
require 'new_relic/agent/instrumentation/rails3/errors'

class Api::V1::BaseController < ActionController::Metal
	include ActionController::Instrumentation
	include ActionController::Rescue
	
	# ...
	
	# In order to enable NewRelic RPM monitoring in the API we'll need to include it
	include NewRelic::Agent::Instrumentation::ControllerInstrumentation
	include NewRelic::Agent::Instrumentation::Rails3::ActionController
	include NewRelic::Agent::Instrumentation::Rails3::Errors
		
end

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NewRelic RPM with ActionController::Metal