yabeda-rails浅析

继承::Rails::Railtie，使其在rails项目中自动执行::Yabeda::Rails.install!

# yabeda-rails-0.8.1/lib/yabeda/rails/railtie.rb
module Yabeda
  module Rails
    class Railtie < ::Rails::Railtie
      def rails_server?
        ::Rails.const_defined?(:Server)
      end

      def puma_server?
        ::Rails.const_defined?("Puma::CLI")
      end

      def unicorn_server?
        ::Rails.const_defined?("Unicorn::Launcher")
      end

      initializer "yabeda-rails.metrics" do
        ::Yabeda::Rails.install! if rails_server? || puma_server? || unicorn_server?
      end
    end
  end
end

而::Yabeda::Rails.install!会使用[[ActiveSupport Notifications]]收集以下指标

# yabeda-rails-0.8.1/lib/yabeda/rails.rb
def install!
  Yabeda.configure do
    config = Config.new
    group :rails
    counter   :requests_total #...
    histogram :request_duration # ...
    histogram :view_runtime # ...
    histogram :db_runtime # ...

    # ...

    ActiveSupport::Notifications.subscribe "process_action.action_controller" do |*args|
      event = ActiveSupport::Notifications::Event.new(*args)
      labels = {
        # ...
      }
      labels.merge!(event.payload.slice(*Yabeda.default_tags.keys - labels.keys))

      rails_requests_total.increment(labels)
      rails_request_duration.measure(labels, Yabeda::Rails.ms2s(event.duration))
      rails_view_runtime.measure(labels, Yabeda::Rails.ms2s(event.payload[:view_runtime]))
      rails_db_runtime.measure(labels, Yabeda::Rails.ms2s(event.payload[:db_runtime]))

      Yabeda::Rails.controller_handlers.each do |handler|
        handler.call(event, labels)
      end
    end
  end
end