Configure gitlab-metrics-exporter logs

This is not in use yet, but we should already
pass in the correct settings.

metrics_server/metrics_server.rb

@@ -40,7 +40,8 @@ def start_for_sidekiq(**options)
     def spawn(target, metrics_dir:, **options)
       return spawn_ruby_server(target, metrics_dir: metrics_dir, **options) unless new_metrics_server?
 
-      settings = settings_for(target)
+      name = settings_key(target)
+      settings = ::Settings.monitoring[name]
       path = options[:path]&.then { |p| Pathname.new(p) } || Pathname.new('')
       cmd = path.join('gitlab-metrics-exporter').to_path
       env = {
@@ -50,6 +51,13 @@ def spawn(target, metrics_dir:, **options)
         'GME_SERVER_PORT' => settings['port'].to_s
       }
 
+      if settings['log_enabled']
+        env['GME_LOG_FILE'] = File.join(Rails.root, 'log', "#{name}.log")
+        env['GME_LOG_LEVEL'] = 'info'
+      else
+        env['GME_LOG_LEVEL'] = 'quiet'
+      end
+
       Process.spawn(env, cmd, err: $stderr, out: $stdout, pgroup: true).tap do |pid|
         Process.detach(pid)
       end
@@ -104,14 +112,12 @@ def ensure_valid_target!(target)
       raise "Target must be one of [puma,sidekiq]" unless %w(puma sidekiq).include?(target)
     end
 
-    def settings_for(target)
-      settings_key =
-        case target
-        when 'puma' then 'web_exporter'
-        when 'sidekiq' then 'sidekiq_exporter'
-        else ensure_valid_target!(target)
-        end
-      ::Settings.monitoring[settings_key]
+    def settings_key(target)
+      case target
+      when 'puma' then 'web_exporter'
+      when 'sidekiq' then 'sidekiq_exporter'
+      else ensure_valid_target!(target)
+      end
     end
   end
 

spec/metrics_server/metrics_server_spec.rb

@@ -97,18 +97,38 @@
         end
 
         context 'for Golang server' do
+          let(:log_enabled) { false }
+          let(:settings) do
+            {
+              'web_exporter' => {
+                'enabled' => true,
+                'address' => 'localhost',
+                'port' => '8083',
+                'log_enabled' => log_enabled
+              },
+              'sidekiq_exporter' => {
+                'enabled' => true,
+                'address' => 'localhost',
+                'port' => '8082',
+                'log_enabled' => log_enabled
+              }
+            }
+          end
+
           let(:expected_port) { target == 'puma' ? '8083' : '8082' }
           let(:expected_env) do
             {
               'GME_MMAP_METRICS_DIR' => metrics_dir,
               'GME_PROBES' => 'self,mmap',
               'GME_SERVER_HOST' => 'localhost',
-              'GME_SERVER_PORT' => expected_port
+              'GME_SERVER_PORT' => expected_port,
+              'GME_LOG_LEVEL' => 'quiet'
             }
           end
 
           before do
             stub_env('GITLAB_GOLANG_METRICS_SERVER', '1')
+            allow(::Settings).to receive(:monitoring).and_return(settings)
           end
 
           it 'spawns a new server process and returns its PID' do
@@ -133,6 +153,24 @@
 
             described_class.spawn(target, metrics_dir: metrics_dir, path: '/path/to/gme/')
           end
+
+          context 'when logs are enabled' do
+            let(:log_enabled) { true }
+            let(:expected_log_file) { target == 'puma' ? 'web_exporter.log' : 'sidekiq_exporter.log' }
+
+            it 'sets log related environment variables' do
+              expect(Process).to receive(:spawn).with(
+                expected_env.merge(
+                  'GME_LOG_LEVEL' => 'info',
+                  'GME_LOG_FILE' => File.join(Rails.root, 'log', expected_log_file)
+                ),
+                'gitlab-metrics-exporter',
+                hash_including(pgroup: true)
+              ).and_return(99)
+
+              described_class.spawn(target, metrics_dir: metrics_dir)
+            end
+          end
         end
       end
     end