OTel Memory Leak

[tjsampson]

Description

Memory Leak in otel library code.

Environment

• OS: Linux
• Architecture: x86
• Go Version: 1.23.2
  - go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.56.0
  • go.opentelemetry.io/otel v1.31.0
  • go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.31.0
  • go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.31.0
  • go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.31.0
  • go.opentelemetry.io/otel/sdk v1.31.0
  • go.opentelemetry.io/otel/trace v1.31.0

Steps To Reproduce

See Comment here: #5190 (comment)

I am pretty sure this is still an issue or something else in the golang otel ecosystem. I will get a pprof setup possibly tomorrow, but here's some anecdotal evidence I have:

Pretty easy to see when tracing was implemented from that graph. And yes. I have removed our tracing implementation and it's back to normal memory usage.

Here is a rough draft of our setup. Please let me know if I am doing anything egregiously dumb, but for the most part, it's all pretty standard stuff take from various docs:

go.mod

go 1.23.2

require (
	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.56.0
	go.opentelemetry.io/otel v1.31.0
	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.31.0
	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.31.0
	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.31.0
	go.opentelemetry.io/otel/sdk v1.31.0
	go.opentelemetry.io/otel/trace v1.31.0
)

We are wrapping the otelhttp.NewHandler around the toplevel muxer, so everything is traced. Yes, I know this is expensive, but it shouldn't leak memory. Eventually we will change this to include/exclude/drop stuff, just so we aren't taking in so much volume (ping routes, health checks, etc.) and do more aggressive down sampling.

func NewApi(c config.Config) *Api {
	return &Api{
		c:           &c,
		controllers: []Controller{newControllers(c)},
		server: &http.Server{
			ReadTimeout:  c.ReadTimeout,
			WriteTimeout: c.WriteTimeout,
			IdleTimeout:  c.IdleTimeout,
			Addr:         fmt.Sprintf(":%d", c.Port),
			Handler:      otelhttp.NewHandler(chi.NewMux(), "INGRESS", otelhttp.WithFilter(traceFilter)),
		},
		done:       make(chan bool),
		sigChannel: make(chan os.Signal, 1024),
	}
}

Here is how we are initializing our trace and metrics providers once on boot:

// TracerProvider an OTLP exporter, and configures the corresponding trace provider.
func TracerProvider(ctx context.Context, res *resource.Resource) (func(context.Context) error, error) {
	// Set up a trace exporter
	traceExporter, err := otlptrace.New(ctx, otlptracegrpc.NewClient())
	if err != nil {
		return nil, errors.Wrap(err, "failed to create trace exporter")
	}

	// Register the trace exporter with a TracerProvider, using a batch
	// span processor to aggregate spans before export.
	tracerProvider := sdktrace.NewTracerProvider(
		sdktrace.WithSampler(sdktrace.AlwaysSample()),
		sdktrace.WithResource(res),
		sdktrace.WithBatcher(traceExporter),
	)
	otel.SetTracerProvider(tracerProvider)
	otel.SetTextMapPropagator(
		propagation.NewCompositeTextMapPropagator(
			propagation.TraceContext{},
			propagation.Baggage{},
		))

	// Shutdown will flush any remaining spans and shut down the exporter.
	return tracerProvider.Shutdown, nil
}

// MeterProvider an OTLP exporter, and configures the corresponding meter provider.
func MeterProvider(ctx context.Context, res *resource.Resource) (func(context.Context) error, error) {
	metricExporter, err := otlpmetricgrpc.New(ctx)
	if err != nil {
		return nil, errors.Wrap(err, "failed to create metric exporter")
	}

	meterProvider := sdkmetric.NewMeterProvider(
		sdkmetric.WithReader(sdkmetric.NewPeriodicReader(metricExporter)),
		sdkmetric.WithResource(res),
	)
	otel.SetMeterProvider(meterProvider)

	return meterProvider.Shutdown, nil
}

Then called and shutdown on main:

	shutDownTracer, err := traceinstrument.TracerProvider(ctx, traceRes)
	if err != nil {
		log.Logger.Fatal("failed to create trace provider", zap.Error(err))
	}
	
	defer func(onShutdown func(ctx context.Context) error) {
		if errr := onShutdown(ctx); errr != nil {
			log.Logger.Error("error shutting down trace provider", zap.Error(errr))
		}
	}(shutDownTracer)

	shutdownTraceMetrics, err := traceinstrument.MeterProvider(ctx, traceRes)
	if err != nil {
		log.Logger.Fatal("failed to create meter provider", zap.Error(err))
	}

	defer func(onShutdown func(ctx context.Context) error) {
		if errr := onShutdown(ctx); errr != nil {
			log.Logger.Error("error shutting down metrics provider", zap.Error(errr))
		}
	}(shutdownTraceMetrics)

Note. We are also using the otelhttp.NewTransport to wrap the default logging transport:

http.DefaultTransport = otelhttp.NewTransport(http.DefaultTransport)

If we remove tracing setup, memory usage goes back to normal. So the leak is definitely in our tracing setup.

Expected behavior

Memory does not continuously increase over time.

[MrAlias]

@tjsampson are you using cumulative temporality (the default IIRC for the metric gRPC exporter)?

Is the cardinality of your metrics unbounded?

[MrAlias]

What is the definition of traceFilter? Does it hold state?

[MrAlias]

Do you have any pprof data for the memory usage?

[tjsampson]

What is the definition of traceFilter? Does it hold state?

func traceFilter(req *http.Request) bool {
	skipTraceAgents := []string{"kube-probe", "ELB-HealthChecker"}
	ua := req.UserAgent()

	for _, skipAgent := range skipTraceAgents {
		if strings.Contains(ua, skipAgent) {
			return false
		}
	}
	return true
}

Possibly the issue?

[tjsampson]

@tjsampson are you using cumulative temporality (the default IIRC for the metric gRPC exporter)?

Yes. We are using the default.

[tjsampson]

Is the cardinality of your metrics unbounded?

No, they aren't unbounded. We aren't actually using the otel meter provider for any custom metrics (still using prometheus for that). We are using it for the default metrics so that we can link metrics to traces inside Grafana. So, unless the default metrics are unbounded, we should be safe (no custom metrics).

[MrAlias]

What is the definition of traceFilter? Does it hold state?

func traceFilter(req *http.Request) bool {
	skipTraceAgents := []string{"kube-probe", "ELB-HealthChecker"}
	ua := req.UserAgent()

	for _, skipAgent := range skipTraceAgents {
		if strings.Contains(ua, skipAgent) {
			return false
		}
	}
	return true
}

Possibly the issue?

I don't see a way for this to grow. Guessing this isn't the issue.

[MrAlias]

Are you able to collect pprof memory data? It's is hard to say where the allocations are going at this point without it.

[tjsampson]

@MrAlias The leak is pretty slow. We just deployed the service a couple of days ago, as seen in the graph, but its steadily climbing. I've been making tweaks/changes to that code. I will post what we are currently running, just for posterity.

[tjsampson]

main.go

	var (
		ctx, cancel = context.WithCancel(context.Background())
		cfg         = config.Boot()
		err         error
	)
	defer cancel()

        traceRes, err := traceinstrument.TraceResource(ctx)
	if err != nil {
		log.Logger.Panic("failed to create trace resource", zap.Error(err))
	}

	shutDownTracer, err := traceinstrument.TracerProvider(ctx, traceRes)
	if err != nil {
		log.Logger.Panic("failed to create trace provider", zap.Error(err))
	}

	defer func(onShutdown func(ctx context.Context) error) {
		if errr := onShutdown(ctx); errr != nil {
			log.Logger.Error("error shutting down trace provider", zap.Error(errr))
		}
	}(shutDownTracer)

	shutdownTraceMetrics, err := traceinstrument.MeterProvider(ctx, traceRes)
	if err != nil {
		log.Logger.Panic("failed to create meter provider", zap.Error(err))
	}

	defer func(onShutdown func(ctx context.Context) error) {
		if errr := onShutdown(ctx); errr != nil {
			log.Logger.Error("error shutting down metrics provider", zap.Error(errr))
		}
	}(shutdownTraceMetrics)

        .... do other stuff.....

instrument.go

func TraceResource(ctx context.Context) (*resource.Resource, error) {
	var (
		ciEnv            = os.Getenv("CI_ENVIRONMENT") 
		cloudEnvironment = os.Getenv("CLOUD_ENVIRONMENT") 
		attribs          = []attribute.KeyValue{serviceName, serviceVersion}
	)
	if ciEnv != "" {
		attribs = append(attribs, attribute.String("environment.ci", ciEnv))
	}
	if cloudEnvironment != "" {
		attribs = append(attribs, attribute.String("environment.cloud", cloudEnvironment))
	}

	return resource.New(ctx, resource.WithAttributes(attribs...))
}

// TracerProvider an OTLP exporter, and configures the corresponding trace provider.
func TracerProvider(ctx context.Context, res *resource.Resource) (func(context.Context) error, error) {
	// If not enabled, use a no-op tracer provider.
	if !tracingEnabled() {
		log.Logger.Warn("ENABLE_TRACING false, using noop tracer provider")
		tp := traceNoop.NewTracerProvider()
		otel.SetTracerProvider(tp)
		return func(ctx context.Context) error {
			return nil
		}, nil
	}

	// Set up a trace exporter
	traceExporter, err := otlptrace.New(ctx, otlptracegrpc.NewClient())
	if err != nil {
		return nil, errors.Wrap(err, "failed to create trace exporter")
	}

	// Register the trace exporter with a TracerProvider, using a batch
	// span processor to aggregate spans before export.
	tracerProvider := sdktrace.NewTracerProvider(
		sdktrace.WithSampler(sdktrace.AlwaysSample()),
		sdktrace.WithResource(res),
		sdktrace.WithBatcher(traceExporter),
	)
	otel.SetTracerProvider(tracerProvider)
	otel.SetTextMapPropagator(
		propagation.NewCompositeTextMapPropagator(
			propagation.TraceContext{},
			propagation.Baggage{},
		))


	// Shutdown will flush any remaining spans and shut down the exporter.
	return tracerProvider.Shutdown, nil
}

// MeterProvider an OTLP exporter, and configures the corresponding meter provider.
func MeterProvider(ctx context.Context, res *resource.Resource) (func(context.Context) error, error) {
	// If not enabled, use a no-op meter provider.
	if !tracingEnabled() {
		log.Logger.Warn("ENABLE_TRACING false, using noop meter provider")
		mp := metricNoop.NewMeterProvider()
		otel.SetMeterProvider(mp)
		return func(ctx context.Context) error {
			return nil
		}, nil
	}

	metricExporter, err := otlpmetricgrpc.New(ctx)
	if err != nil {
		return nil, errors.Wrap(err, "failed to create metric exporter")
	}

	meterProvider := sdkmetric.NewMeterProvider(
		sdkmetric.WithReader(sdkmetric.NewPeriodicReader(metricExporter)),
		sdkmetric.WithResource(res),
	)
	otel.SetMeterProvider(meterProvider)

	return meterProvider.Shutdown, nil
}

func tracingEnabled() bool {
	traceEnabled := os.Getenv("ENABLE_TRACING")
	enabled, err := strconv.ParseBool(traceEnabled)
	if err != nil {
		return false
	}
	return enabled
}

func CloudCustomerSpanEvent(ctx context.Context, evt string) {
	span := trace.SpanFromContext(ctx)
	bag := baggage.FromContext(ctx)
	tc := attribute.Key("customer")
	cust := bag.Member("customer")
	span.AddEvent(evt, trace.WithAttributes(tc.String(cust.Value())))
}

server.go

		server := &http.Server{
			ReadHeaderTimeout: time.Second * 5, 
			ReadTimeout:       c.ReadTimeout,
			WriteTimeout:      c.WriteTimeout,
			IdleTimeout:       c.IdleTimeout,
			Addr:              fmt.Sprintf(":%d", c.Port),
			Handler:           otelhttp.NewHandler(chi.NewMux(), "INGRESS"),
		},

go.mod

	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.58.0
	go.opentelemetry.io/otel v1.32.0
	go.opentelemetry.io/otel/trace v1.32.0
         go.opentelemetry.io/contrib/propagators/b3 v1.32.0
	go.opentelemetry.io/otel v1.32.0
	go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc v1.32.0
	go.opentelemetry.io/otel/exporters/otlp/otlptrace v1.32.0
	go.opentelemetry.io/otel/exporters/otlp/otlptrace/otlptracegrpc v1.32.0
	go.opentelemetry.io/otel/metric v1.32.0
	go.opentelemetry.io/otel/sdk v1.32.0
	go.opentelemetry.io/otel/sdk/metric v1.32.0

[tjsampson]

I've got this hooked up to Grafana Pyroscope and doing some continuous profiling. It typically takes a few days for the leak to really show itself, just because of how slow it is. From what I can tell early on is that it seems to be around these calls:

- go.opentelemetry.io/otel/sdk/metric/exemplar.newStorage
- google.golang.org/grpc/mem.NewTieredBufferPool.newSizedBufferPool
- go.opentelemetry.io/otel/sdk/trace.NewBatchSpanProcessor

I am going to try and get some heap dumps periodically over the next few days. However, given that it's the Holidays, I am not sure if the lower levels of volume/traffic in these test/dev environments will produce the same effect, so might have to wait until after the new year.