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

AssetPath with ActionController::Metal

Damian Galarza — Mon, 13 Aug 2012 02:26:53 -0400

At QFive we’re building an API to serve our iOS application and throughout the site for ajax requests. Since our API only serves JSON we could slim down our controllers being used for the API to speed up requests as much as possible. In order to achieve this we’ve built a base controller for our API which inherits from ActionController::Metal instead of ActionController::Base. I was originally introduced to this idea in the book “Crafting Rails Applications” by Jose Valim.

One issue we’ve run into we’ve run into is related to the asset pipeline and serving assets from a custom asset host.

For example:

config/environments/production.rb

Example::Application.configure do
	config.action_controller.asset_host = "//static.example/com"
end

Typically the usage behind this in a rails application is masked, whenever you use image_tag the image will be routed to the asset host on its own behind the scenes. However since we’re inheriting from ActionController::Base there is some work to be done. We’ll need to include a couple of modules and ensure that the load hooks are loaded in our base controller, something that happens behind the scenes when inheriting from ActionController::Base.

class Api::V1::BaseController < ActionController::Metal
	include AbstractController::AssetPaths
	
	include ActionController::Redirecting
	include ActionController::Rendering
	include ActionController::Caching
	include ActionController::Renderers::All
	include ActionController::ConditionalGet
	include ActionController::ParamsWrapper
	include ActionController::MimeResponds
	
	ActiveSupport.run_load_hooks(:action_controller, self)
end

Of course, depending on what your application is using your mileage may vary. Our actual API BaseController looks something more like:

class Api::V1::BaseController < ActionController::Metal
	include AbstractController::AssetPaths
	include ActionController::Helpers

	include ActionController::Redirecting
	include ActionController::Rendering
	include ActionController::Caching
	include ActionController::Renderers::All
	include ActionController::ConditionalGet
	include ActionController::ParamsWrapper

	include ActionController::MimeResponds
	include ActionController::RequestForgeryProtection
	include AbstractController::Callbacks

	include ActionController::Instrumentation
	include ActionController::Rescue

	Rails.application.routes.default_url_options = ActionMailer::Base.default_url_options
	include Rails.application.routes.url_helpers

	append_view_path "#{Rails.root}/app/views"

	protect_from_forgery

	ActiveSupport.run_load_hooks(:action_controller, self)
end

Be sure to check out the rails ActionController::Base to see what else is included by default and tweak as you see fit.

Actioncontroller-Metal on Damian Galarza | Software Engineering & AI Consulting

NewRelic RPM with ActionController::Metal

AssetPath with ActionController::Metal