Add prometheous endpoints for reporting metrics

Add prometheous endpoints for reporting metrics

app/controllers/projects/ci/prometheus_metrics/histograms_controller.rb

+# frozen_string_literal: true
+
+module Projects
+  module Ci
+    module PrometheusMetrics
+      class HistogramsController < Projects::ApplicationController
+        feature_category :pipeline_authoring
+
+        respond_to :json, only: [:create]
+
+        def create
+          result = ::Ci::PrometheusMetrics::ObserveHistogramsService.new(project, permitted_params).execute
+
+          render json: result.body, status: result.status
+        end
+
+        private
+
+        def permitted_params
+          params.permit(histograms: [:name, :value])
+        end
+      end
+    end
+  end
+end

app/services/ci/prometheus_metrics/observe_histograms_service.rb

+# frozen_string_literal: true
+
+module Ci
+  module PrometheusMetrics
+    class ObserveHistogramsService
+      Result = Struct.new(:status, :body, keyword_init: true)
+
+      class << self
+        def available_histograms
+          @available_histograms ||= [
+            histogram(:pipeline_graph_link_calculation_duration_seconds, 'Total time spent calculating links, in seconds', {}, [0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.8, 1, 2]),
+            histogram(:pipeline_graph_links_total, 'Number of links per graph', {}, [1, 5, 10, 25, 50, 100, 200]),
+            histogram(:pipeline_graph_link_per_job_ratio, 'Ratio of links to job per graph', {}, [0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1])
+          ].to_h
+        end
+
+        private
+
+        def histogram(name, *attrs)
+          [name.to_s, proc { Gitlab::Metrics.histogram(name, *attrs) }]
+        end
+      end
+
+      def initialize(project, params)
+        @project = project
+        @params = params
+      end
+
+      def execute
+        return Result.new(status: 202, body: {}) unless enabled?
+
+        params
+          .fetch(:histograms, [])
+          .each(&method(:observe))
+
+        Result.new(status: 201, body: {})
+      end
+
+      private
+
+      attr_reader :project, :params
+
+      def observe(data)
+        histogram = find_histogram(data[:name])
+        histogram.observe({ project: project.full_path }, data[:value].to_f)
+      end
+
+      def find_histogram(name)
+        self.class.available_histograms
+          .fetch(name) { raise ActiveRecord::RecordNotFound }
+          .call
+      end
+
+      def enabled?
+        ::Feature.enabled?(:ci_accept_frontend_prometheus_metrics, project, default_enabled: :yaml)
+      end
+    end
+  end
+end

config/feature_flags/development/ci_accept_frontend_prometheus_metrics.yml

+---
+name: ci_accept_frontend_prometheus_metrics
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/52820
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/300770
+milestone: '13.9'
+type: development
+group: group::pipeline authoring
+default_enabled: false

config/routes/project.rb

@@ -87,6 +87,9 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
           resource :lint, only: [:show, :create]
           resource :pipeline_editor, only: [:show], controller: :pipeline_editor, path: 'editor'
           resources :daily_build_group_report_results, only: [:index], constraints: { format: /(csv|json)/ }
+          namespace :prometheus_metrics do
+            resources :histograms, only: [:create], constraints: { format: 'json' }
+          end
         end
 
         namespace :settings do

doc/administration/monitoring/prometheus/gitlab_metrics.md

@@ -119,6 +119,9 @@ The following metrics are available:
 | `gitlab_external_http_duration_seconds`                        | Counter   |  13.8 | Duration in seconds spent on each HTTP call to external systems                                       |                                                         |
 | `gitlab_external_http_exception_total`                         | Counter   |  13.8 | Total number of exceptions raised when making external HTTP calls                                     |                                                         |
 | `ci_report_parser_duration_seconds`                            | Histogram |  13.9 | Time to parse CI/CD report artifacts                                                                  | `parser`                                                |
+| `pipeline_graph_link_calculation_duration_seconds`             | Histogram |  13.9 | Total time spent calculating links, in seconds                                                        | `project`                                               |
+| `pipeline_graph_links_total`                                   | Histogram |  13.9 | Number of links per graph                                                                             | `project`                                               |
+| `pipeline_graph_link_per_job_ratio`                            | Histogram |  13.9 | Ratio of links to job per graph                                                                       | `project`                                               |
 
 ## Metrics controlled by a feature flag
 

spec/requests/projects/ci/promeheus_metrics/histograms_controller_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe 'Projects::Ci::PrometheusMetrics::HistogramsController' do
+  let_it_be(:project) { create(:project, :public) }
+
+  describe 'POST /*namespace_id/:project_id/-/ci/prometheus_metrics/histograms' do
+    context 'with known histograms' do
+      it 'returns 201 Created' do
+        post histograms_route(histograms: [
+          { name: :pipeline_graph_link_calculation_duration_seconds, value: 1 },
+          { name: :pipeline_graph_links_total, value: 10 }
+        ])
+
+        expect(response).to have_gitlab_http_status(:created)
+      end
+    end
+
+    context 'with unknown histograms' do
+      it 'returns 404 Not Found' do
+        post histograms_route(histograms: [{ name: :chunky_bacon, value: 5 }])
+
+        expect(response).to have_gitlab_http_status(:not_found)
+      end
+    end
+  end
+
+  def histograms_route(params = {})
+    namespace_project_ci_prometheus_metrics_histograms_path(namespace_id: project.namespace, project_id: project, **params)
+  end
+end

spec/services/ci/prometheus_metrics/observe_histograms_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Ci::PrometheusMetrics::ObserveHistogramsService do
+  let_it_be(:project) { create(:project) }
+  let(:params) { {} }
+
+  subject(:execute) { described_class.new(project, params).execute }
+
+  before do
+    Gitlab::Metrics.reset_registry!
+  end
+
+  context 'with empty data' do
+    it 'does not raise errors' do
+      expect(subject.status).to eq(201)
+    end
+  end
+
+  context 'observes metrics successfully' do
+    let(:params) do
+      {
+        histograms: [
+          { name: 'pipeline_graph_link_calculation_duration_seconds', value: '1' },
+          { name: 'pipeline_graph_link_per_job_ratio', value: '0.9' }
+        ]
+      }
+    end
+
+    it 'increments the metrics' do
+      execute
+
+      expect(histogram_data).to match(a_hash_including({ 0.8 => 0.0, 1 => 1.0, 2 => 1.0 }))
+
+      expect(histogram_data(:pipeline_graph_link_per_job_ratio))
+        .to match(a_hash_including({ 0.8 => 0.0, 0.9 => 1.0, 1 => 1.0 }))
+    end
+
+    it 'returns an empty body and status code' do
+      expect(subject.status).to eq(201)
+      expect(subject.body).to eq({})
+    end
+  end
+
+  context 'with unknown histograms' do
+    let(:params) do
+      { histograms: [{ name: 'chunky_bacon', value: '4' }] }
+    end
+
+    it 'raises ActiveRecord::RecordNotFound error' do
+      expect { subject }.to raise_error ActiveRecord::RecordNotFound
+    end
+  end
+
+  context 'with feature flag disabled' do
+    before do
+      stub_feature_flags(ci_accept_frontend_prometheus_metrics: false)
+    end
+
+    let(:params) do
+      {
+        histograms: [
+          { name: 'pipeline_graph_link_calculation_duration_seconds', value: '4' }
+        ]
+      }
+    end
+
+    it 'does not register the metrics' do
+      execute
+
+      expect(histogram_data).to be_nil
+    end
+
+    it 'returns an empty body and status code' do
+      expect(subject.status).to eq(202)
+      expect(subject.body).to eq({})
+    end
+  end
+
+  def histogram_data(name = :pipeline_graph_link_calculation_duration_seconds)
+    Gitlab::Metrics.registry.get(name)&.get({ project: project.full_path })
+  end
+end