use IMetricsRecorder consistently and fall back to Noop

Signed-off-by: Florian Bacher <florian.bacher@dynatrace.com>

core/pkg/telemetry/builder.go

@@ -43,7 +43,7 @@ func RegisterErrorHandling(log *logger.Logger) {
 // BuildMetricsRecorder is a helper to build telemetry.MetricsRecorder based on configurations
 func BuildMetricsRecorder(
 	ctx context.Context, svcName string, svcVersion string, config Config,
-) (*MetricsRecorder, error) {
+) (IMetricsRecorder, error) {
 	// Build metric reader based on configurations
 	mReader, err := buildMetricReader(ctx, config)
 	if err != nil {

flagd/pkg/service/flag-evaluation/connect_service.go

@@ -57,7 +57,7 @@ func (b bufSwitchHandler) ServeHTTP(writer http.ResponseWriter, request *http.Re
 type ConnectService struct {
 	logger                *logger.Logger
 	eval                  evaluator.IEvaluator
-	metrics               *telemetry.MetricsRecorder
+	metrics               telemetry.IMetricsRecorder
 	eventingConfiguration IEvents
 
 	server        *http.Server
@@ -71,17 +71,21 @@ type ConnectService struct {
 
 // NewConnectService creates a ConnectService with provided parameters
 func NewConnectService(
-	logger *logger.Logger, evaluator evaluator.IEvaluator, mRecorder *telemetry.MetricsRecorder,
+	logger *logger.Logger, evaluator evaluator.IEvaluator, mRecorder telemetry.IMetricsRecorder,
 ) *ConnectService {
-	return &ConnectService{
+	cs := &ConnectService{
 		logger:  logger,
 		eval:    evaluator,
-		metrics: mRecorder,
+		metrics: &telemetry.NoopMetricsRecorder{},
 		eventingConfiguration: &eventingConfiguration{
 			subs: make(map[interface{}]chan service.Notification),
 			mu:   &sync.RWMutex{},
 		},
 	}
+	if mRecorder != nil {
+		cs.metrics = mRecorder
+	}
+	return cs
 }
 
 // Serve serves services with provided configuration options
@@ -183,16 +187,14 @@ func (s *ConnectService) setupServer(svcConf service.Configuration) (net.Listene
 	s.serverMtx.Unlock()
 
 	// Add middlewares
-	if s.metrics != nil {
-		metricsMiddleware := metricsmw.NewHTTPMetric(metricsmw.Config{
-			Service:        svcConf.ServiceName,
-			MetricRecorder: s.metrics,
-			Logger:         s.logger,
-			HandlerID:      "",
-		})
-
-		s.AddMiddleware(metricsMiddleware)
-	}
+	metricsMiddleware := metricsmw.NewHTTPMetric(metricsmw.Config{
+		Service:        svcConf.ServiceName,
+		MetricRecorder: s.metrics,
+		Logger:         s.logger,
+		HandlerID:      "",
+	})
+
+	s.AddMiddleware(metricsMiddleware)
 
 	corsMiddleware := corsmw.New(svcConf.CORS)
 	s.AddMiddleware(corsMiddleware)

flagd/pkg/service/flag-evaluation/flag_evaluator.go

@@ -36,7 +36,7 @@ type OldFlagEvaluationService struct {
 
 // NewOldFlagEvaluationService creates a OldFlagEvaluationService with provided parameters
 func NewOldFlagEvaluationService(log *logger.Logger,
-	eval evaluator.IEvaluator, eventingCfg IEvents, metricsRecorder *telemetry.MetricsRecorder,
+	eval evaluator.IEvaluator, eventingCfg IEvents, metricsRecorder telemetry.IMetricsRecorder,
 ) *OldFlagEvaluationService {
 	svc := &OldFlagEvaluationService{
 		logger:                log,
@@ -73,9 +73,8 @@ func (s *OldFlagEvaluationService) ResolveAll(
 	span.SetAttributes(attribute.Int("feature_flag.count", len(values)))
 	for _, value := range values {
 		// register the impression and reason for each flag evaluated
-		if s.metrics != nil {
-			s.metrics.RecordEvaluation(sCtx, value.Error, value.Reason, value.Variant, value.FlagKey)
-		}
+		s.metrics.RecordEvaluation(sCtx, value.Error, value.Reason, value.Variant, value.FlagKey)
+
 		switch v := value.Value.(type) {
 		case bool:
 			res.Flags[value.FlagKey] = &schemaV1.AnyFlag{

flagd/pkg/service/middleware/metrics/http_metrics.go

@@ -16,7 +16,7 @@ import (
 )
 
 type Config struct {
-	MetricRecorder     *telemetry.MetricsRecorder
+	MetricRecorder     telemetry.IMetricsRecorder
 	Logger             *logger.Logger
 	Service            string
 	GroupedStatus      bool
@@ -41,7 +41,7 @@ func (cfg *Config) defaults() {
 		log.Fatal("missing logger")
 	}
 	if cfg.MetricRecorder == nil {
-		cfg.Logger.Fatal("missing OpenTelemetry metric recorder")
+		cfg.MetricRecorder = &telemetry.NoopMetricsRecorder{}
 	}
 }