New Relic log http_referer on every request

Question

We have this beofre_filter in application controller in order to log the HTTP_REFER in first place

  def init_newrelic_agent
      ::NewRelic::Agent.add_custom_parameters(
        request_referer: request.referer,
        request_url: request.url,
        request_user_agent: request.user_agent
      )
    end

This adds the above custom parameters only if the request lands in the rails controller. However some requests don't even land there, because they hit our app with the false route for example. How would you configure rails to log this params in newrelic on every application trace even if some errors occur before even the controller is initialized?

Answer 1

For those who interested, below the concrete implementation:

#config/initializers/newrelic.rb
Rails.configuration.middleware.use  NewRelic::Rack::Custom  

#app/middlewares/newrelic/rack/custom.rb
module NewRelic
  module Rack

    class Custom
      def initialize(app)
        @app = app
      end

      def call(env)
        init_newrelic_agent(env)
        @app.call(env)
      end

      def init_newrelic_agent(env)
        ::NewRelic::Agent.add_custom_parameters(
          request_referer: env['HTTP_REFERER'],
          request_url: env['REQUEST_URI'],
          request_user_agent: env['HTTP_USER_AGENT']
        )
      end

    end
  end
end

Answer 2

Versions of the New Relic Ruby agent from 3.9.0 on can track transactions in Rack middlewares, so adding your own middleware where you include these parameters could work you if these requests aren't hitting a Rails controller. Rack::Request is a good option for this type of middleware addition.