lib/gitlab/middleware/rails_queue_duration.rb


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# frozen_string_literal: true

# This Rack middleware is intended to measure the latency between
# gitlab-workhorse forwarding a request to the Rails application and the
# time this middleware is reached.

module Gitlab
  module Middleware
    class RailsQueueDuration
      GITLAB_RAILS_QUEUE_DURATION_KEY = 'GITLAB_RAILS_QUEUE_DURATION'

      def initialize(app)
        @app = app
      end

      def call(env)
        trans = Gitlab::Metrics.current_transaction
        proxy_start = env['HTTP_GITLAB_WORKHORSE_PROXY_START'].presence
        if trans && proxy_start
          # Time in milliseconds since gitlab-workhorse started the request
          duration = Time.now.to_f * 1_000 - proxy_start.to_f / 1_000_000
          trans.set(:rails_queue_duration, duration)
          metric_rails_queue_duration_seconds.observe(trans.labels, duration / 1_000)
          env[GITLAB_RAILS_QUEUE_DURATION_KEY] = duration.round(2)
        end

        @app.call(env)
      end

      private

      def metric_rails_queue_duration_seconds
        @metric_rails_queue_duration_seconds ||= Gitlab::Metrics.histogram(
          :gitlab_rails_queue_duration_seconds,
          Gitlab::Metrics::Transaction::BASE_LABELS
        )
      end
    end
  end
end