Instrument CI parsers

Prepends a new module into each CI report parser to add
histogram tracking for duration of parsing task.

changelogs/unreleased/eb-prometheus-monitoring-report-parsers.yml

+---
+title: Instrument CI parsers
+merge_request: 51241
+author:
+type: added

config/initializers/7_prometheus_metrics.rb

@@ -53,6 +53,8 @@ if !Rails.env.test? && Gitlab::Metrics.prometheus_metrics_enabled?
     if Gitlab.ee? && Gitlab::Runtime.sidekiq?
       Gitlab::Metrics::Samplers::GlobalSearchSampler.instance.start
     end
+
+    Gitlab::Ci::Parsers.instrument!
   rescue IOError => e
     Gitlab::ErrorTracking.track_exception(e)
     Gitlab::Metrics.error_detected!
@@ -72,6 +74,8 @@ if !Rails.env.test? && Gitlab::Metrics.prometheus_metrics_enabled?
     unless Gitlab::Runtime.sidekiq?
       Gitlab::Metrics::RequestsRackMiddleware.initialize_metrics
     end
+
+    Gitlab::Ci::Parsers.instrument!
   rescue IOError => e
     Gitlab::ErrorTracking.track_exception(e)
     Gitlab::Metrics.error_detected!

lib/gitlab/ci/parsers.rb

@@ -20,6 +20,10 @@ module Gitlab
       rescue KeyError
         raise ParserNotFoundError, "Cannot find any parser matching file type '#{file_type}'"
       end
+
+      def self.instrument!
+        parsers.values.each { |parser_class| parser_class.prepend(Parsers::Instrumentation) }
+      end
     end
   end
 end

lib/gitlab/ci/parsers/instrumentation.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Ci
+    module Parsers
+      module Instrumentation
+        BUCKETS = [0.25, 1, 5, 10].freeze
+
+        def parse!(*args)
+          parser_result = nil
+
+          duration = Benchmark.realtime do
+            parser_result = super
+          end
+
+          labels = {}
+
+          histogram = Gitlab::Metrics.histogram(
+            :ci_report_parser_duration_seconds,
+            'Duration of parsing a CI report artifact',
+            labels,
+            BUCKETS
+          )
+
+          histogram.observe({ parser: self.class.name }, duration)
+
+          parser_result
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/ci/parsers/instrumentation_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Ci::Parsers::Instrumentation do
+  describe '#parse!' do
+    let(:parser_class) do
+      Class.new do
+        prepend Gitlab::Ci::Parsers::Instrumentation
+
+        def parse!(arg1, arg2)
+          "parse #{arg1} #{arg2}"
+        end
+      end
+    end
+
+    it 'sets metrics for duration of parsing' do
+      result = parser_class.new.parse!('hello', 'world')
+
+      expect(result).to eq('parse hello world')
+
+      metrics = Gitlab::Metrics.registry.get(:ci_report_parser_duration_seconds).get({ parser: parser_class.name })
+
+      expect(metrics.keys).to match_array(described_class::BUCKETS)
+    end
+  end
+end

spec/lib/gitlab/ci/parsers_spec.rb

@@ -54,4 +54,12 @@ RSpec.describe Gitlab::Ci::Parsers do
       end
     end
   end
+
+  describe '.instrument!' do
+    it 'prepends the Instrumentation module into each parser' do
+      expect(described_class.parsers.values).to all( receive(:prepend).with(Gitlab::Ci::Parsers::Instrumentation) )
+
+      described_class.instrument!
+    end
+  end
 end