config_initializers_scout_apm_active_job.rb

# A module for instrumenting ActiveJob workers for Scout APM.
#
# These can appear under "Background Jobs" (default) or "Web Endpoints" in the UI, depending on the value of
# +SCOUT_TRANSACTION_TYPE+.
#
# Example usage:
#
# class BaseJob < ActiveJob::Base
#
#   def perform(attributes)
#     # Do work
#   end
#   # This MUST be included AFTER the perform method is defined.
#   include ScoutApm::BackgroundJobIntegrations::ActiveJob::Instruments
# end
#

module ScoutApm
  module BackgroundJobIntegrations
    class ActiveJob
      module Instruments
        SCOUT_TRANSACTION_TYPE = 'Job'
        def self.included(instrumented_class)
          ScoutApm::Agent.instance.logger.debug "Instrumenting #{instrumented_class.inspect}"
          instrumented_class.class_eval do
            unless instrumented_class.method_defined?(:perform_without_scout_instruments)
              alias_method :perform_without_scout_instruments, :perform
              alias_method :perform, :perform_with_scout_instruments
            end
          end
        end

        def perform_with_scout_instruments(*args)
          ensure_scout_started!
          req = ScoutApm::RequestManager.lookup

          started_queue = false

          if scout_job_transaction?
            req.start_layer(ScoutApm::Layer.new('Queue', self.queue_name))
            started_queue = true
          end

          req.start_layer(ScoutApm::Layer.new(SCOUT_TRANSACTION_TYPE, scout_job_name))
          started_transaction = true

          begin
            perform_without_scout_instruments(*args)
          rescue
            req.error!
            raise
          ensure
            req.stop_layer if started_transaction
            req.stop_layer if started_queue
          end
        end

        def scout_job_name
          self.class.to_s
        end

        def scout_job_transaction?
          SCOUT_TRANSACTION_TYPE == 'Job'
        end

        def ensure_scout_started!
          unless ScoutApm::Agent.instance.background_worker_running?
            ScoutApm::Agent.instance.start(skip_app_server_check: true)
            ScoutApm::Agent.instance.start_background_worker
          end
        end
      end
    end
  end
end

Rails.application.config.after_initialize do
  ActiveJob::Base.descendants.each do |subclass|
    subclass.include(ScoutApm::BackgroundJobIntegrations::ActiveJob::Instruments)
  end
end