Cart Service

This service maintains items placed in the shopping cart by users. It interacts with a Redis caching service for fast access to shopping cart data.

Cart service source

Note OpenTelemetry for .NET uses the System.Diagnostic.DiagnosticSource library as its API instead of the standard OpenTelemetry API for Traces and Metrics. Microsoft.Extensions.Logging.Abstractions library is used for Logs.

Traces

Initializing Tracing

OpenTelemetry is configured in the .NET dependency injection container. The AddOpenTelemetry() builder method is used to configure desired instrumentation libraries, add exporters, and set other options. Configuration of the exporter and resource attributes is performed through environment variables.

Action<ResourceBuilder> appResourceBuilder =
    resource => resource
        .AddDetector(new ContainerResourceDetector())
        .AddDetector(new HostDetector());

builder.Services.AddOpenTelemetry()
    .ConfigureResource(appResourceBuilder)
    .WithTracing(tracerBuilder => tracerBuilder
        .AddRedisInstrumentation(
            cartStore.GetConnection(),
            options => options.SetVerboseDatabaseStatements = true)
        .AddAspNetCoreInstrumentation()
        .AddGrpcClientInstrumentation()
        .AddHttpClientInstrumentation()
        .AddOtlpExporter());

Add attributes to auto-instrumented spans

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

var activity = Activity.Current;

Adding attributes (tags in .NET) to a span (activity) is accomplished using SetTag on the activity object. In the AddItem function from services/CartService.cs several attributes are added to the auto-instrumented span.

activity?.SetTag("app.user.id", request.UserId);
activity?.SetTag("app.product.quantity", request.Item.Quantity);
activity?.SetTag("app.product.id", request.Item.ProductId);

Add span events

Adding span (activity) events is accomplished using AddEvent on the activity object. In the GetCart function from services/CartService.cs a span event is added.

activity?.AddEvent(new("Fetch cart"));

Metrics

Initializing Metrics

Similar to configuring OpenTelemetry Traces, the .NET dependency injection container requires a call to AddOpenTelemetry(). This builder configures desired instrumentation libraries, exporters, etc.

Action<ResourceBuilder> appResourceBuilder =
    resource => resource
        .AddDetector(new ContainerResourceDetector());

builder.Services.AddOpenTelemetry()
    .ConfigureResource(appResourceBuilder)
    .WithMetrics(meterBuilder => meterBuilder
        .AddProcessInstrumentation()
        .AddRuntimeInstrumentation()
        .AddAspNetCoreInstrumentation()
        .AddOtlpExporter());

Logs

Logs are configured in the .NET dependency injection container on LoggingBuilder level by calling AddOpenTelemetry(). This builder configures desired options, exporters, etc.

builder.Logging
    .AddOpenTelemetry(options => options.AddOtlpExporter());