Allow enabling Prometheus metrics via ENV variable when db is seeded

db/fixtures/production/010_settings.rb

-if ENV['GITLAB_SHARED_RUNNERS_REGISTRATION_TOKEN'].present?
-  settings = ApplicationSetting.current || ApplicationSetting.create_from_defaults
-  settings.set_runners_registration_token(ENV['GITLAB_SHARED_RUNNERS_REGISTRATION_TOKEN'])
-
+def save(settings, topic)
   if settings.save
-    puts "Saved Runner Registration Token".color(:green)
+    puts "Saved #{topic}".color(:green)
   else
-    puts "Could not save Runner Registration Token".color(:red)
+    puts "Could not save #{topic}".color(:red)
     puts
     settings.errors.full_messages.map do |message|
       puts "--> #{message}".color(:red)
     end
     puts
-    exit 1
+    exit(1)
+  end
+end
+
+envs = %w{ GITLAB_PROMETHEUS_METRICS_ENABLED GITLAB_SHARED_RUNNERS_REGISTRATION_TOKEN }
+
+if envs.any? {|env_name| ENV[env_name].present? }
+  settings = ApplicationSetting.current || ApplicationSetting.create_from_defaults
+  if ENV['GITLAB_SHARED_RUNNERS_REGISTRATION_TOKEN'].present?
+    settings.set_runners_registration_token(ENV['GITLAB_SHARED_RUNNERS_REGISTRATION_TOKEN'])
+    save(settings, 'Runner Registration Token')
+  end
+
+  if ENV['GITLAB_PROMETHEUS_METRICS_ENABLED'].present?
+    value = Gitlab::Utils.to_boolean(ENV['GITLAB_PROMETHEUS_METRICS_ENABLED'])
+    settings.prometheus_metrics_enabled = value
+    save(settings, 'GITLAB_PROMETHEUS_METRICS_ENABLED')
   end
 end

spec/db/production/settings_spec.rb

+require 'spec_helper'
+require 'rainbow/ext/string'
+
+describe 'seed production settings', lib: true do
+  include StubENV
+  let(:settings_file) { File.join(__dir__, '../../../db/fixtures/production/010_settings.rb') }
+  let(:settings) { ApplicationSetting.current || ApplicationSetting.create_from_defaults }
+
+  context 'GITLAB_SHARED_RUNNERS_REGISTRATION_TOKEN is set in the environment' do
+    before do
+      stub_env('GITLAB_SHARED_RUNNERS_REGISTRATION_TOKEN', '013456789')
+    end
+
+    it 'writes the token to the database' do
+      load(settings_file)
+
+      expect(settings.runners_registration_token).to eq('013456789')
+    end
+  end
+
+  context 'GITLAB_PROMETHEUS_METRICS_ENABLED is set in the environment' do
+    context 'GITLAB_PROMETHEUS_METRICS_ENABLED is true' do
+      before do
+        stub_env('GITLAB_PROMETHEUS_METRICS_ENABLED', 'true')
+      end
+
+      it 'prometheus_metrics_enabled is set to true ' do
+        load(settings_file)
+
+        expect(settings.prometheus_metrics_enabled).to eq(true)
+      end
+    end
+
+    context 'GITLAB_PROMETHEUS_METRICS_ENABLED is false' do
+      before do
+        stub_env('GITLAB_PROMETHEUS_METRICS_ENABLED', 'false')
+      end
+
+      it 'prometheus_metrics_enabled is set to false' do
+        load(settings_file)
+
+        expect(settings.prometheus_metrics_enabled).to eq(false)
+      end
+    end
+  end
+end