Convert rails_queue_duration to metric_rails_queue_duration_seconds

lib/gitlab/middleware/rails_queue_duration.rb

@@ -14,11 +14,22 @@ module Gitlab
         proxy_start = env['HTTP_GITLAB_WORKHORSE_PROXY_START'].presence
         if trans && proxy_start
           # Time in milliseconds since gitlab-workhorse started the request
-          trans.set(:rails_queue_duration, Time.now.to_f * 1_000 - proxy_start.to_f / 1_000_000)
+          duration = Time.now.to_f * 1_000 - proxy_start.to_f / 1_000_000
+          trans.set(:rails_queue_duration, duration)
+          self.class.metric_rails_queue_duration_seconds.observe(trans.labels, duration / 1_000)
         end
 
         @app.call(env)
       end
+
+      private
+
+      def self.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

spec/lib/gitlab/middleware/rails_queue_duration_spec.rb

@@ -4,7 +4,7 @@ describe Gitlab::Middleware::RailsQueueDuration do
   let(:app) { double(:app) }
   let(:middleware) { described_class.new(app) }
   let(:env) { {} }
-  let(:transaction) { double(:transaction) }
+  let(:transaction) { Gitlab::Metrics::Transaction.new(env) }
 
   before do
     expect(app).to receive(:call).with(env).and_return('yay')
@@ -30,6 +30,16 @@ describe Gitlab::Middleware::RailsQueueDuration do
         expect(transaction).to receive(:set).with(:rails_queue_duration, an_instance_of(Float))
         expect(middleware.call(env)).to eq('yay')
       end
+
+      it 'observes rails queue duration metrics and calls the app when the header is present' do
+        env['HTTP_GITLAB_WORKHORSE_PROXY_START'] = '2000000000'
+
+        expect(described_class.metric_rails_queue_duration_seconds).to receive(:observe).with(transaction.labels, 1)
+
+        Timecop.freeze(Time.at(3)) do
+          expect(middleware.call(env)).to eq('yay')
+        end
+      end
     end
   end
 end