productcatalogservice.md

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))
    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.UnaryInterceptor(otelgrpc.UnaryServerInterceptor()),
        grpc.StreamInterceptor(otelgrpc.StreamServerInterceptor()),
    )

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.WithUnaryInterceptor(otelgrpc.UnaryClientInterceptor()),
        grpc.WithStreamInterceptor(otelgrpc.StreamClientInterceptor()),
    )
}

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

TBD

Logs

TBD