checkoutservice.md

Checkout Service

This service is responsible to process a checkout order from the user. The checkout service will call many other services in order to process an order.

Checkout 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.Fatal(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.Printf("Error shutting down tracer provider: %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.

    var srv = grpc.NewServer(
        grpc.UnaryInterceptor(otelgrpc.UnaryServerInterceptor()),
        grpc.StreamInterceptor(otelgrpc.StreamServerInterceptor()),
    )

This service will issue several 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 PlaceOrder function several attributes are added to the span.

    span.SetAttributes(
        attribute.String("app.order.id", orderID.String()), shippingTrackingAttribute,
        attribute.Float64("app.shipping.amount", shippingCostFloat),
        attribute.Float64("app.order.amount", totalPriceFloat),
        attribute.Int("app.order.items.count", len(prep.orderItems)),
    )

Add span events

Adding span events is accomplished using AddEvent on the span object. In the PlaceOrder function several span events are added. Some events have additional attributes, others do not.

Adding a span event without attributes:

    span.AddEvent("prepared")

Adding a span event with additional attributes:

    span.AddEvent("charged",
        trace.WithAttributes(attribute.String("app.payment.transaction.id", txID)))

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 MeterProvider.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.Printf("Error shutting down meter provider: %v", err)
        }
    }()

Adding golang runtime auto-instrumentation

Golang runtime are instrumented in the main function

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

Logs

TBD