Add certificate_based_clusters FF to Service Ping

We want to have an idea if self-managed users will be turning this FF
off before we completely remove the feature that's behind the FF.

In this commit we:

- Add the metric YAML definition under settings key_path
- Add the Instrumentation class
- Add specs

Changelog: other

config/metrics/settings/20220222181654_certificate_based_clusters_ff.yml

+---
+key_path: settings.certificate_based_clusters_ff
+name: "certificate_based_clusters_ff"
+description: "Certificate-based clusters feature flag"
+product_section: ops
+product_stage: configure
+product_group: group::configure
+product_category:
+value_type: boolean
+status: active
+milestone: "14.9"
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/81311
+time_frame: none
+data_source: database
+data_category: optional
+instrumentation_class: CertBasedClustersFfMetric
+performance_indicator_type: []
+distribution:
+- ce
+- ee
+tier:
+- free
+- premium
+- ultimate

lib/gitlab/usage/metrics/instrumentations/cert_based_clusters_ff_metric.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Usage
+    module Metrics
+      module Instrumentations
+        class CertBasedClustersFfMetric < GenericMetric
+          value do
+            Feature.enabled?(:certificate_based_clusters, default_enabled: :yaml, type: :ops)
+          end
+        end
+      end
+    end
+  end
+end

lib/gitlab/usage_data.rb

@@ -224,7 +224,8 @@ module Gitlab
             collected_data_categories: add_metric('CollectedDataCategoriesMetric', time_frame: 'none'),
             service_ping_features_enabled: add_metric('ServicePingFeaturesMetric', time_frame: 'none'),
             snowplow_enabled: add_metric('SnowplowEnabledMetric', time_frame: 'none'),
-            snowplow_configured_to_gitlab_collector: add_metric('SnowplowConfiguredToGitlabCollectorMetric', time_frame: 'none')
+            snowplow_configured_to_gitlab_collector: add_metric('SnowplowConfiguredToGitlabCollectorMetric', time_frame: 'none'),
+            certificate_based_clusters_ff: add_metric('CertBasedClustersFfMetric')
           }
         }
       end

spec/lib/gitlab/usage/metrics/instrumentations/cert_based_clusters_ff_metric_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Usage::Metrics::Instrumentations::CertBasedClustersFfMetric do
+  context 'with FF enabled' do
+    it_behaves_like 'a correct instrumented metric value', { time_frame: '7d', data_source: 'database' } do
+      let(:expected_value) { true }
+    end
+  end
+
+  context 'with FF disabled' do
+    before do
+      stub_feature_flags(certificate_based_clusters: false)
+    end
+
+    it_behaves_like 'a correct instrumented metric value', { time_frame: '7d', data_source: 'database' } do
+      let(:expected_value) { false }
+    end
+  end
+end

spec/lib/gitlab/usage_data_spec.rb

@@ -1100,6 +1100,20 @@ RSpec.describe Gitlab::UsageData, :aggregate_failures do
         expect(subject[:settings][:user_cap_feature_enabled]).to eq(Gitlab::CurrentSettings.new_user_signups_cap)
       end
 
+      it 'reports status of the certificate_based_clusters feature flag as true' do
+        expect(subject[:settings][:certificate_based_clusters_ff]).to eq(true)
+      end
+
+      context 'with certificate_based_clusters disabled' do
+        before do
+          stub_feature_flags(certificate_based_clusters: false)
+        end
+
+        it 'reports status of the certificate_based_clusters feature flag as false' do
+          expect(subject[:settings][:certificate_based_clusters_ff]).to eq(false)
+        end
+      end
+
       context 'snowplow stats' do
         before do
           stub_feature_flags(usage_data_instrumentation: false)