[service] Replace telemetryInitializer by MeterProvider wrapper (#9454)

**Description:** 

Refactor meter provider initialization; removes `telemetryInitializer`
and replaces it by a MeterProvider wrapper that owns the lifetime of the
OpenCensus registry and the servers associated with the MeterProvider.

**Link to tracking Issue:** Relates to #4970 (first refactor before
trying out the factory pattern in an internal package)

service/service.go

@@ -65,12 +65,10 @@ type Settings struct {
 
 // Service represents the implementation of a component.Host.
 type Service struct {
-	buildInfo            component.BuildInfo
-	telemetry            *telemetry.Telemetry
-	telemetrySettings    servicetelemetry.TelemetrySettings
-	host                 *serviceHost
-	telemetryInitializer *telemetryInitializer
-	collectorConf        *confmap.Conf
+	buildInfo         component.BuildInfo
+	telemetrySettings servicetelemetry.TelemetrySettings
+	host              *serviceHost
+	collectorConf     *confmap.Conf
 }
 
 func New(ctx context.Context, set Settings, cfg Config) (*Service, error) {
@@ -87,43 +85,48 @@ func New(ctx context.Context, set Settings, cfg Config) (*Service, error) {
 			buildInfo:         set.BuildInfo,
 			asyncErrorChannel: set.AsyncErrorChannel,
 		},
-		telemetryInitializer: newColTelemetry(disableHighCard, extendedConfig),
-		collectorConf:        set.CollectorConf,
+		collectorConf: set.CollectorConf,
 	}
-	var err error
-	srv.telemetry, err = telemetry.New(ctx, telemetry.Settings{BuildInfo: set.BuildInfo, ZapOptions: set.LoggingOptions}, cfg.Telemetry)
+	tel, err := telemetry.New(ctx, telemetry.Settings{BuildInfo: set.BuildInfo, ZapOptions: set.LoggingOptions}, cfg.Telemetry)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get logger: %w", err)
 	}
 	res := resource.New(set.BuildInfo, cfg.Telemetry.Resource)
 	pcommonRes := pdataFromSdk(res)
 
-	logger := srv.telemetry.Logger()
-	if err = srv.telemetryInitializer.init(res, logger, cfg.Telemetry, set.AsyncErrorChannel); err != nil {
-		return nil, fmt.Errorf("failed to initialize telemetry: %w", err)
+	logger := tel.Logger()
+	mp, err := newMeterProvider(
+		meterProviderSettings{
+			res:               res,
+			logger:            logger,
+			cfg:               cfg.Telemetry.Metrics,
+			asyncErrorChannel: set.AsyncErrorChannel,
+		},
+		disableHighCard,
+		extendedConfig,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create metric provider: %w", err)
 	}
 	srv.telemetrySettings = servicetelemetry.TelemetrySettings{
 		Logger:         logger,
-		TracerProvider: srv.telemetry.TracerProvider(),
-		MeterProvider:  srv.telemetryInitializer.mp,
+		MeterProvider:  mp,
+		TracerProvider: tel.TracerProvider(),
 		MetricsLevel:   cfg.Telemetry.Metrics.Level,
 		// Construct telemetry attributes from build info and config's resource attributes.
 		Resource: pcommonRes,
 		Status: status.NewReporter(srv.host.notifyComponentStatusChange, func(err error) {
 			if errors.Is(err, status.ErrStatusNotReady) {
-				srv.telemetry.Logger().Warn("Invalid transition", zap.Error(err))
+				logger.Warn("Invalid transition", zap.Error(err))
 			}
 			// ignore other errors as they represent invalid state transitions and are considered benign.
 		}),
 	}
 
 	// process the configuration and initialize the pipeline
 	if err = srv.initExtensionsAndPipeline(ctx, set, cfg); err != nil {
-		// If pipeline initialization fails then shut down the telemetry server
-		if shutdownErr := srv.telemetryInitializer.shutdown(); shutdownErr != nil {
-			err = multierr.Append(err, fmt.Errorf("failed to shutdown collector telemetry: %w", shutdownErr))
-		}
-
+		// If pipeline initialization fails then shut down telemetry
+		err = multierr.Append(err, srv.shutdownTelemetry(ctx))
 		return nil, err
 	}
 
@@ -168,6 +171,28 @@ func (srv *Service) Start(ctx context.Context) error {
 	return nil
 }
 
+func (srv *Service) shutdownTelemetry(ctx context.Context) error {
+	// The metric.MeterProvider and trace.TracerProvider interfaces do not have a Shutdown method.
+	// To shutdown the providers we try to cast to this interface, which matches the type signature used in the SDK.
+	type shutdownable interface {
+		Shutdown(context.Context) error
+	}
+
+	var err error
+	if prov, ok := srv.telemetrySettings.MeterProvider.(shutdownable); ok {
+		if shutdownErr := prov.Shutdown(ctx); shutdownErr != nil {
+			err = multierr.Append(err, fmt.Errorf("failed to shutdown meter provider: %w", shutdownErr))
+		}
+	}
+
+	if prov, ok := srv.telemetrySettings.TracerProvider.(shutdownable); ok {
+		if shutdownErr := prov.Shutdown(ctx); shutdownErr != nil {
+			err = multierr.Append(err, fmt.Errorf("failed to shutdown tracer provider: %w", shutdownErr))
+		}
+	}
+	return err
+}
+
 // Shutdown the service. Shutdown will do the following steps in order:
 // 1. Notify extensions that the pipeline is shutting down.
 // 2. Shutdown all pipelines.
@@ -194,13 +219,8 @@ func (srv *Service) Shutdown(ctx context.Context) error {
 
 	srv.telemetrySettings.Logger.Info("Shutdown complete.")
 
-	if err := srv.telemetry.Shutdown(ctx); err != nil {
-		errs = multierr.Append(errs, fmt.Errorf("failed to shutdown telemetry: %w", err))
-	}
+	errs = multierr.Append(errs, srv.shutdownTelemetry(ctx))
 
-	if err := srv.telemetryInitializer.shutdown(); err != nil {
-		errs = multierr.Append(errs, fmt.Errorf("failed to shutdown collector telemetry: %w", err))
-	}
 	return errs
 }
 
@@ -231,7 +251,7 @@ func (srv *Service) initExtensionsAndPipeline(ctx context.Context, set Settings,
 
 	if cfg.Telemetry.Metrics.Level != configtelemetry.LevelNone && cfg.Telemetry.Metrics.Address != "" {
 		// The process telemetry initialization requires the ballast size, which is available after the extensions are initialized.
-		if err = proctelemetry.RegisterProcessMetrics(srv.telemetryInitializer.mp, getBallastSize(srv.host)); err != nil {
+		if err = proctelemetry.RegisterProcessMetrics(srv.telemetrySettings.MeterProvider, getBallastSize(srv.host)); err != nil {
 			return fmt.Errorf("failed to register process metrics: %w", err)
 		}
 	}

service/telemetry.go

@@ -29,57 +29,46 @@ const (
 	zapKeyTelemetryLevel   = "level"
 )
 
-type telemetryInitializer struct {
+type meterProvider struct {
+	*sdkmetric.MeterProvider
 	ocRegistry *ocmetric.Registry
-	mp         metric.MeterProvider
 	servers    []*http.Server
-
-	disableHighCardinality bool
-	extendedConfig         bool
 }
 
-func newColTelemetry(disableHighCardinality bool, extendedConfig bool) *telemetryInitializer {
-	return &telemetryInitializer{
-		mp:                     noopmetric.NewMeterProvider(),
-		disableHighCardinality: disableHighCardinality,
-		extendedConfig:         extendedConfig,
-	}
+type meterProviderSettings struct {
+	res               *resource.Resource
+	logger            *zap.Logger
+	cfg               telemetry.MetricsConfig
+	asyncErrorChannel chan error
 }
 
-func (tel *telemetryInitializer) init(res *resource.Resource, logger *zap.Logger, cfg telemetry.Config, asyncErrorChannel chan error) error {
-	if cfg.Metrics.Level == configtelemetry.LevelNone || (cfg.Metrics.Address == "" && len(cfg.Metrics.Readers) == 0) {
-		logger.Info(
+func newMeterProvider(set meterProviderSettings, disableHighCardinality bool, extendedConfig bool) (metric.MeterProvider, error) {
+	if set.cfg.Level == configtelemetry.LevelNone || (set.cfg.Address == "" && len(set.cfg.Readers) == 0) {
+		set.logger.Info(
 			"Skipping telemetry setup.",
-			zap.String(zapKeyTelemetryAddress, cfg.Metrics.Address),
-			zap.String(zapKeyTelemetryLevel, cfg.Metrics.Level.String()),
+			zap.String(zapKeyTelemetryAddress, set.cfg.Address),
+			zap.String(zapKeyTelemetryLevel, set.cfg.Level.String()),
 		)
-		return nil
+		return noopmetric.NewMeterProvider(), nil
 	}
 
-	logger.Info("Setting up own telemetry...")
-	return tel.initMetrics(res, logger, cfg, asyncErrorChannel)
-}
-
-func (tel *telemetryInitializer) initMetrics(res *resource.Resource, logger *zap.Logger, cfg telemetry.Config, asyncErrorChannel chan error) error {
-	// Initialize the ocRegistry, still used by the process metrics.
-	tel.ocRegistry = ocmetric.NewRegistry()
-
-	if len(cfg.Metrics.Address) != 0 {
-		if tel.extendedConfig {
-			logger.Warn("service::telemetry::metrics::address is being deprecated in favor of service::telemetry::metrics::readers")
+	set.logger.Info("Setting up own telemetry...")
+	if len(set.cfg.Address) != 0 {
+		if extendedConfig {
+			set.logger.Warn("service::telemetry::metrics::address is being deprecated in favor of service::telemetry::metrics::readers")
 		}
-		host, port, err := net.SplitHostPort(cfg.Metrics.Address)
+		host, port, err := net.SplitHostPort(set.cfg.Address)
 		if err != nil {
-			return err
+			return nil, err
 		}
 		portInt, err := strconv.Atoi(port)
 		if err != nil {
-			return err
+			return nil, err
 		}
-		if cfg.Metrics.Readers == nil {
-			cfg.Metrics.Readers = []config.MetricReader{}
+		if set.cfg.Readers == nil {
+			set.cfg.Readers = []config.MetricReader{}
 		}
-		cfg.Metrics.Readers = append(cfg.Metrics.Readers, config.MetricReader{
+		set.cfg.Readers = append(set.cfg.Readers, config.MetricReader{
 			Pull: &config.PullMetricReader{
 				Exporter: config.MetricExporter{
 					Prometheus: &config.Prometheus{
@@ -91,41 +80,47 @@ func (tel *telemetryInitializer) initMetrics(res *resource.Resource, logger *zap
 		})
 	}
 
-	metricproducer.GlobalManager().AddProducer(tel.ocRegistry)
+	mp := &meterProvider{
+		// Initialize the ocRegistry, still used by the process metrics.
+		ocRegistry: ocmetric.NewRegistry(),
+	}
+	metricproducer.GlobalManager().AddProducer(mp.ocRegistry)
 	opts := []sdkmetric.Option{}
-	for _, reader := range cfg.Metrics.Readers {
+	for _, reader := range set.cfg.Readers {
 		// https://github.com/open-telemetry/opentelemetry-collector/issues/8045
-		r, server, err := proctelemetry.InitMetricReader(context.Background(), reader, asyncErrorChannel)
+		r, server, err := proctelemetry.InitMetricReader(context.Background(), reader, set.asyncErrorChannel)
 		if err != nil {
-			return err
+			return nil, err
 		}
 		if server != nil {
-			tel.servers = append(tel.servers, server)
-			logger.Info(
+			mp.servers = append(mp.servers, server)
+			set.logger.Info(
 				"Serving metrics",
 				zap.String(zapKeyTelemetryAddress, server.Addr),
-				zap.String(zapKeyTelemetryLevel, cfg.Metrics.Level.String()),
+				zap.String(zapKeyTelemetryLevel, set.cfg.Level.String()),
 			)
 		}
 		opts = append(opts, sdkmetric.WithReader(r))
 	}
 
-	mp, err := proctelemetry.InitOpenTelemetry(res, opts, tel.disableHighCardinality)
+	var err error
+	mp.MeterProvider, err = proctelemetry.InitOpenTelemetry(set.res, opts, disableHighCardinality)
 	if err != nil {
-		return err
+		return nil, err
 	}
-	tel.mp = mp
-	return nil
+	return mp, nil
 }
 
-func (tel *telemetryInitializer) shutdown() error {
-	metricproducer.GlobalManager().DeleteProducer(tel.ocRegistry)
+// Shutdown the meter provider and all the associated resources.
+// The type signature of this method matches that of the sdkmetric.MeterProvider.
+func (mp *meterProvider) Shutdown(ctx context.Context) error {
+	metricproducer.GlobalManager().DeleteProducer(mp.ocRegistry)
 
 	var errs error
-	for _, server := range tel.servers {
+	for _, server := range mp.servers {
 		if server != nil {
 			errs = multierr.Append(errs, server.Close())
 		}
 	}
-	return errs
+	return multierr.Append(errs, mp.MeterProvider.Shutdown(ctx))
 }

service/telemetry_test.go

@@ -275,8 +275,6 @@ func TestTelemetryInit(t *testing.T) {
 		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
-			tel := newColTelemetry(tc.disableHighCard, tc.extendedConfig)
-			buildInfo := component.NewDefaultBuildInfo()
 			if tc.extendedConfig {
 				tc.cfg.Metrics.Readers = []config.MetricReader{
 					{
@@ -299,19 +297,26 @@ func TestTelemetryInit(t *testing.T) {
 					},
 				}
 			}
-			otelRes := resource.New(buildInfo, tc.cfg.Resource)
-			err := tel.init(otelRes, zap.NewNop(), *tc.cfg, make(chan error))
+			set := meterProviderSettings{
+				res:               resource.New(component.NewDefaultBuildInfo(), tc.cfg.Resource),
+				logger:            zap.NewNop(),
+				cfg:               tc.cfg.Metrics,
+				asyncErrorChannel: make(chan error),
+			}
+			mp, err := newMeterProvider(set, tc.disableHighCard, tc.extendedConfig)
 			require.NoError(t, err)
 			defer func() {
-				require.NoError(t, tel.shutdown())
+				if prov, ok := mp.(interface{ Shutdown(context.Context) error }); ok {
+					require.NoError(t, prov.Shutdown(context.Background()))
+				}
 			}()
 
-			v := createTestMetrics(t, tel.mp)
+			v := createTestMetrics(t, mp)
 			defer func() {
 				view.Unregister(v)
 			}()
 
-			metrics := getMetricsFromPrometheus(t, tel.servers[0].Handler)
+			metrics := getMetricsFromPrometheus(t, mp.(*meterProvider).servers[0].Handler)
 			require.Equal(t, len(tc.expectedMetrics), len(metrics))
 
 			for metricName, metricValue := range tc.expectedMetrics {