unicorn_connection_monitor.rb

require "raindrops"

class UnicornConnectionMonitor
  def initialize(app, options = {})
    @app = app
    @statsd = options.fetch(:statsd)
  end

  def call(env)
    if linux? && unicorn?
      Raindrops::Linux.tcp_listener_stats(tcp_listeners).each do |_, stats|
        @statsd.measure("unicorn.connections.active", stats.active)
        @statsd.measure("unicorn.connections.queued", stats.queued)
      end
    end

    @app.call(env)
  end

  private

  def tcp_listeners
    @tcp_listeners ||= Unicorn.listener_names.grep(/\A.+:\d+\z/)
  end

  def linux?
    @linux ||= defined?(Raindrops::Linux) &&
      Raindrops::Linux.respond_to?(:tcp_listener_stats)
  end

  def unicorn?
    @unicorn ||= defined?(Unicorn) && Unicorn.respond_to?(:listener_names)
  end
end