Tweak default_alert_setup & add specs

- Unit tests

app/models/project_services/prometheus_service.rb

@@ -24,6 +24,8 @@ class PrometheusService < MonitoringService
 
   after_commit :track_events
 
+  after_create_commit :create_default_alerts
+
   def initialize_properties
     if properties.nil?
       self.properties = {}
@@ -147,4 +149,10 @@ class PrometheusService < MonitoringService
   def disabled_manual_prometheus?
     manual_configuration_changed? && !manual_configuration?
   end
+
+  def create_default_alerts
+    return unless project_id
+
+    Prometheus::CreateDefaultAlertsWorker.perform_async(project_id: project_id)
+  end
 end

app/services/prometheus/create_default_alerts_service.rb

+# frozen_string_literal: true
+
+module Prometheus
+  class CreateDefaultAlertsService < BaseService
+    include Gitlab::Utils::StrongMemoize
+
+    attr_reader :project
+
+    DEFAULT_ALERTS = [
+      {
+        identifier: 'response_metrics_nginx_ingress_16_http_error_rate',
+        operator: 'gt',
+        threshold: 0.1
+      },
+      {
+        identifier: 'response_metrics_nginx_ingress_http_error_rate',
+        operator: 'gt',
+        threshold: 0.1
+      }
+    ].freeze
+
+    def initialize(project:)
+      @project = project
+    end
+
+    def execute
+      return ServiceResponse.error(message: 'Invalid project') unless project
+      return ServiceResponse.error(message: 'Invalid environment') unless environment
+
+      create_alerts
+
+      ServiceResponse.success
+    end
+
+    private
+
+    def create_alerts
+      DEFAULT_ALERTS.each do |alert_hash|
+        identifier = alert_hash[:identifier]
+        next if alerts_by_identifier(environment).key?(identifier)
+
+        metric = metrics_by_identifier[identifier]
+        next unless metric
+
+        create_alert(alert: alert_hash, metric: metric)
+      end
+    end
+
+    def metrics_by_identifier
+      strong_memoize(:metrics_by_identifier) do
+        metric_identifiers = DEFAULT_ALERTS.map { |alert| alert[:identifier] }
+
+        PrometheusMetricsFinder
+          .new(identifier: metric_identifiers, common: true)
+          .execute
+          .index_by(&:identifier)
+      end
+    end
+
+    def alerts_by_identifier(environment)
+      strong_memoize(:alerts_by_identifier) do
+        Projects::Prometheus::AlertsFinder
+          .new(project: project, metric: metrics_by_identifier.values, environment: environment)
+          .execute
+          .index_by { |alert| alert.prometheus_metric.identifier }
+      end
+    end
+
+    def environment
+      strong_memoize(:environment) do
+        EnvironmentsFinder.new(project, nil, name: 'production').find.first ||
+          project.environments.first
+      end
+    end
+
+    def create_alert(alert:, metric:)
+      PrometheusAlert.create!(
+        project: project,
+        prometheus_metric: metric,
+        environment: environment,
+        threshold: alert[:threshold],
+        operator: alert[:operator]
+      )
+    rescue ActiveRecord::RecordNotUnique
+      # Ignore duplicate creations although it unlikely to happen
+    end
+  end
+end

app/workers/all_queues.yml

@@ -1256,6 +1256,13 @@
   :resource_boundary: :unknown
   :weight: 1
   :idempotent: 
+- :name: prometheus_create_default_alerts
+  :feature_category: :incident_management
+  :has_external_dependencies: 
+  :urgency: :high
+  :resource_boundary: :unknown
+  :weight: 1
+  :idempotent: true
 - :name: propagate_service_template
   :feature_category: :source_code_management
   :has_external_dependencies: 

app/workers/prometheus/create_default_alerts_worker.rb

+# frozen_string_literal: true
+
+module Prometheus
+  class CreateDefaultAlertsWorker
+    include ApplicationWorker
+
+    feature_category :incident_management
+    urgency :high
+    idempotent!
+
+    def perform(project_id)
+      project = Project.find_by_id(project_id)
+
+      return unless project
+
+      result = Prometheus::CreateDefaultAlertsService.new(project: project).execute
+
+      log_info(result.message) if result.error?
+    end
+
+    private
+
+    def log_info(message)
+      logger.info(structured_payload(message: message))
+    end
+  end
+end

changelogs/unreleased/118788-automatic-metric-alerts.yml

+---
+title: Add Prometheus alerts automatically after Prometheus Service was created
+merge_request: 28503
+author:
+type: added

config/sidekiq_queues.yml

@@ -200,6 +200,8 @@
   - 1
 - - project_update_repository_storage
   - 1
+- - prometheus_create_default_alerts
+  - 1
 - - propagate_service_template
   - 1
 - - reactive_caching

spec/models/project_services/prometheus_service_spec.rb

@@ -123,6 +123,34 @@ describe PrometheusService, :use_clean_rails_memory_store_caching do
     end
   end
 
+  describe 'callbacks' do
+    context 'after_create' do
+      let(:project) { create(:project) }
+      let(:service) { build(:prometheus_service, project: project) }
+
+      subject(:create_service) { service.save! }
+
+      it 'creates default alerts' do
+        expect(Prometheus::CreateDefaultAlertsWorker)
+          .to receive(:perform_async)
+          .with(project_id: project.id)
+
+        create_service
+      end
+
+      context 'no project exists' do
+        let(:service) { build(:prometheus_service, :instance) }
+
+        it 'does not create default alerts' do
+          expect(Prometheus::CreateDefaultAlertsWorker)
+            .not_to receive(:perform_async)
+
+          create_service
+        end
+      end
+    end
+  end
+
   describe '#test' do
     before do
       service.manual_configuration = true

spec/services/prometheus/create_default_alerts_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Prometheus::CreateDefaultAlertsService do
+  let_it_be(:project) { create(:project) }
+  let(:instance) { described_class.new(project: project) }
+  let(:expected_alerts) { described_class::DEFAULT_ALERTS }
+
+  describe '#execute' do
+    subject(:execute) { instance.execute }
+
+    shared_examples 'no alerts created' do
+      it 'does not create alerts' do
+        expect { execute }.not_to change { project.reload.prometheus_alerts.count }
+      end
+    end
+
+    context 'no environment' do
+      it_behaves_like 'no alerts created'
+    end
+
+    context 'environment exists' do
+      let_it_be(:environment) { create(:environment, project: project) }
+
+      context 'no found metric' do
+        it_behaves_like 'no alerts created'
+      end
+
+      context 'metric exists' do
+        before do
+          create_expected_metrics!
+        end
+
+        context 'alert exists already' do
+          before do
+            create_pre_existing_alerts!(environment)
+          end
+
+          it_behaves_like 'no alerts created'
+        end
+
+        it 'creates alerts' do
+          expect { execute }.to change { project.reload.prometheus_alerts.count }
+           .by(expected_alerts.size)
+        end
+
+        context 'multiple environments' do
+          let!(:production) { create(:environment, project: project, name: 'production') }
+
+          it 'uses the production environment' do
+            expect { execute }.to change { production.reload.prometheus_alerts.count }
+              .by(expected_alerts.size)
+          end
+        end
+      end
+    end
+  end
+
+  private
+
+  def create_expected_metrics!
+    expected_alerts.each do |alert_hash|
+      create(:prometheus_metric, :common, identifier: alert_hash.fetch(:identifier))
+    end
+  end
+
+  def create_pre_existing_alerts!(environment)
+    expected_alerts.each do |alert_hash|
+      metric = PrometheusMetric.for_identifier(alert_hash[:identifier]).first!
+      create(:prometheus_alert, prometheus_metric: metric, project: project, environment: environment)
+    end
+  end
+end

spec/workers/prometheus/create_default_alerts_worker_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Prometheus::CreateDefaultAlertsWorker do
+  let_it_be(:project) { create(:project) }
+  let(:worker) { described_class.new }
+  let(:logger) { worker.send(:logger) }
+  let(:service) { instance_double(Prometheus::CreateDefaultAlertsService) }
+  let(:service_result) { ServiceResponse.success }
+
+  subject { described_class.new.perform(project.id) }
+
+  before do
+    allow(Prometheus::CreateDefaultAlertsService)
+      .to receive(:new).with(project: project)
+      .and_return(service)
+    allow(service).to receive(:execute)
+      .and_return(service_result)
+  end
+
+  it_behaves_like 'an idempotent worker' do
+    let(:job_args) { [project.id] }
+
+    it 'calls the service' do
+      expect(service).to receive(:execute)
+
+      subject
+    end
+
+    context 'project is nil' do
+      let(:job_args) { [nil] }
+
+      it 'does not call the service' do
+        expect(service).not_to receive(:execute)
+
+        subject
+      end
+    end
+
+    context 'when service returns an error' do
+      let(:error_message) { 'some message' }
+      let(:service_result) { ServiceResponse.error(message: error_message) }
+
+      it 'succeeds and logs the error' do
+        expect(logger)
+          .to receive(:info)
+          .with(a_hash_including('message' => error_message))
+          .exactly(worker_exec_times).times
+
+        subject
+      end
+    end
+  end
+
+  context 'when service raises an exception' do
+    let(:error_message) { 'some exception' }
+    let(:exception) { StandardError.new(error_message) }
+
+    it 're-raises exception' do
+      allow(service).to receive(:execute).and_raise(exception)
+
+      expect { subject }.to raise_error(exception)
+    end
+  end
+end