Product Catalog Service

This service is responsible to return information about products. The service can be used to get all products, search for specific products, or return details about any single product.

Product Catalog service source

Traces

Initializing Tracing

The OpenTelemetry SDK is initialized from main using the initTracerProvider function.

func initTracerProvider() *sdktrace.TracerProvider {
    ctx := context.Background()

    exporter, err := otlptracegrpc.New(ctx)
    if err != nil {
        log.Fatalf("OTLP Trace gRPC Creation: %v", err)
    }
    tp := sdktrace.NewTracerProvider(
        sdktrace.WithBatcher(exporter),
        sdktrace.WithResource(initResource()),
    )
    otel.SetTracerProvider(tp)
    otel.SetTextMapPropagator(propagation.NewCompositeTextMapPropagator(propagation.TraceContext{}, propagation.Baggage{}))
    return tp
}

You should call TracerProvider.Shutdown() when your service is shutdown to ensure all spans are exported. This service makes that call as part of a deferred function in main

tp := InitTracerProvider()
defer func() {
    if err := tp.Shutdown(context.Background()); err != nil {
        log.Fatalf("Tracer Provider Shutdown: %v", err)
    }
}()

Adding gRPC auto-instrumentation

This service receives gRPC requests, which are instrumented in the main function as part of the gRPC server creation.

srv := grpc.NewServer(
    grpc.StatsHandler(otelgrpc.NewServerHandler()),
)

This service will issue outgoing gRPC calls, which are all instrumented by wrapping the gRPC client with instrumentation.

func createClient(ctx context.Context, svcAddr string) (*grpc.ClientConn, error) {
    return grpc.DialContext(ctx, svcAddr,
        grpc.WithTransportCredentials(insecure.NewCredentials()),
        grpc.WithStatsHandler(otelgrpc.NewClientHandler()),
    )
}

Add attributes to auto-instrumented spans

Within the execution of auto-instrumented code you can get current span from context.

span := trace.SpanFromContext(ctx)

Adding attributes to a span is accomplished using SetAttributes on the span object. In the GetProduct function an attribute for the product ID is added to the span.

span.SetAttributes(
    attribute.String("app.product.id", req.Id),
)

Setting span status

This service can catch and handle an error condition based on a feature flag. In an error condition, the span status is set accordingly using SetStatus on the span object. You can see this in the GetProduct function.

msg := fmt.Sprintf("Error: ProductCatalogService Fail Feature Flag Enabled")
span.SetStatus(otelcodes.Error, msg)

Add span events

Adding span events is accomplished using AddEvent on the span object. In the GetProduct function a span event is added when an error condition is handled, or when a product is successfully found.

span.AddEvent(msg)

Metrics

Initializing Metrics

The OpenTelemetry SDK is initialized from main using the initMeterProvider function.

func initMeterProvider() *sdkmetric.MeterProvider {
    ctx := context.Background()

    exporter, err := otlpmetricgrpc.New(ctx)
    if err != nil {
        log.Fatalf("new otlp metric grpc exporter failed: %v", err)
    }

    mp := sdkmetric.NewMeterProvider(sdkmetric.WithReader(sdkmetric.NewPeriodicReader(exporter)))
    global.SetMeterProvider(mp)
    return mp
}

You should call initMeterProvider.Shutdown() when your service is shutdown to ensure all records are exported. This service makes that call as part of a deferred function in main.

mp := initMeterProvider()
defer func() {
    if err := mp.Shutdown(context.Background()); err != nil {
        log.Fatalf("Error shutting down meter provider: %v", err)
    }
}()

Adding golang runtime auto-instrumentation

Golang runtime is instrumented in the main function

err := runtime.Start(runtime.WithMinimumReadMemStatsInterval(time.Second))
if err != nil {
    log.Fatal(err)
}

Logs

You can send your logs to the OpenTelemetry Collector in two ways:

• Directly to the Collector
• Through a file or stdout

You can find documentation specifying how to use both these approaches in the Logs section of the Manual Instrumentation documentation.

The Product Catalog service sends the logs directly to the Collector, and uses a log bridge to send its logs, bridging to the slog logging package, which outputs structured logs.

LoggerProvider initialization

The OpenTelemetry SDK is initialized from main using the initLoggerProvider function.

	ctx := context.Background()

	logExporter, err := otlploggrpc.New(ctx)
	if err != nil {
		return nil
	}

	loggerProvider := sdklog.NewLoggerProvider(
		sdklog.WithProcessor(sdklog.NewBatchProcessor(logExporter)),
	)
	global.SetLoggerProvider(loggerProvider)

	return loggerProvider

Call LoggerProvider.Shutdown() when your service is down to ensure all logs are exported. This service makes that call as part of a deferred function in main:

	lp := initLoggerProvider()
	defer func() {
		if err := lp.Shutdown(context.Background()); err != nil {
			logger.Error(fmt.Sprintf("Logger Provider Shutdown: %v", err))
		}
		logger.Info("Shutdown logger provider")
	}()

Logging functionality

This service sends logs to the Collector using gRPC calls. The logs are output in a structured format using the slog package.

First, initialize the logger:

	logger   *slog.Logger
	logger = otelslog.NewLogger("product-catalog")

Note the use of fmt.Sprintf to format the output before it’s sent to the logger:

        logger.Info("Loading Product Catalog...")
        logger.Info(fmt.Sprintf("Product Catalog reload interval: %d", interval))
        logger.Error(fmt.Sprintf("Error shutting down meter provider: %v", err))

The advantage of using slog is the ability to attach additional attributes to the output. The following example attaches the product.name and product.id attributes. This makes it possible to view and parse these as part of the log output and makes it easier to view them as separate columns in Grafana:

	logger.LogAttrs(
		ctx,
		slog.LevelInfo, "Product Found",
		slog.String("app.product.name", found.Name),
		slog.String("app.product.id", req.Id),
	)