add metrics for sidekiq

app/controllers/metrics_controller.rb

@@ -6,12 +6,34 @@ class MetricsController < ActionController::API
   include ActionController::MimeResponds
 
   def show
+    fetch_sidekiq_metrics
+
     render plain: metrics
   end
 
   private
 
+  SIDEKIQ_STATS_METHODS = %i[
+    processed
+    failed
+    scheduled_size
+    retry_size
+    dead_size
+    processes_size
+  ].freeze
+
+  def fetch_sidekiq_metrics
+    stats = Sidekiq::Stats.new
+    SIDEKIQ_STATS_METHODS.each do |key|
+      Retrospring::Metrics::SIDEKIQ[key].set stats.public_send(key)
+    end
+
+    stats.queues.each do |queue, value|
+      Retrospring::Metrics::SIDEKIQ[:queue_enqueued].set value, labels: { queue: }
+    end
+  end
+
   def metrics
-    Prometheus::Client::Formats::Text.marshal(Prometheus::Client.registry)
+    Prometheus::Client::Formats::Text.marshal(Retrospring::Metrics::PROMETHEUS)
   end
 end

lib/retrospring/metrics.rb

@@ -42,5 +42,38 @@ module Retrospring
       :retrospring_comments_created_total,
       docstring: "How many comments got created"
     )
+
+    # metrics from Sidekiq::Stats.new
+    SIDEKIQ = {
+      processed:      gauge(
+        :sidekiq_processed,
+        docstring: "Number of jobs processed by Sidekiq"
+      ),
+      failed:         gauge(
+        :sidekiq_failed,
+        docstring: "Number of jobs that failed"
+      ),
+      scheduled_size: gauge(
+        :sidekiq_scheduled_jobs,
+        docstring: "Number of jobs that are enqueued"
+      ),
+      retry_size:     gauge(
+        :sidekiq_retried_jobs,
+        docstring: "Number of jobs that are being retried"
+      ),
+      dead_size:      gauge(
+        :sidekiq_dead_jobs,
+        docstring: "Number of jobs that are dead"
+      ),
+      processes_size: gauge(
+        :sidekiq_processes,
+        docstring: "Number of active Sidekiq processes"
+      ),
+      queue_enqueued: gauge(
+        :sidekiq_queues_enqueued,
+        docstring: "Number of enqueued jobs per queue",
+        labels:    %i[queue]
+      ),
+    }.freeze
   end
 end

spec/controllers/metrics_controller_spec.rb

@@ -7,9 +7,6 @@ describe MetricsController, type: :controller do
     subject { get :show }
 
     it "returns the metrics" do
-      # ensure we have at least a metric set
-      Retrospring::Metrics::VERSION_INFO.set 1
-
       expect(subject.body).to include "retrospring_version_info"
     end
   end