Observability with the .NET Aspire Dashboard

// ServiceDefaults wires OpenTelemetry for all services in one place

// In Extensions/ServiceDefaultsExtensions.cs (generated by Aspire template):
public static IHostApplicationBuilder AddServiceDefaults(
    this IHostApplicationBuilder builder)
{
    builder.ConfigureOpenTelemetry();
    builder.AddDefaultHealthChecks();
    builder.Services.AddServiceDiscovery();
    builder.Services.ConfigureHttpClientDefaults(http =>
    {
        http.AddStandardResilienceHandler();
        http.AddServiceDiscovery();
    });

    return builder;
}

public static IHostApplicationBuilder ConfigureOpenTelemetry(
    this IHostApplicationBuilder builder)
{
    builder.Logging.AddOpenTelemetry(logging =>
    {
        logging.IncludeFormattedMessage = true;
        logging.IncludeScopes           = true;
    });

    builder.Services.AddOpenTelemetry()
        .WithMetrics(metrics =>
            metrics
                .AddAspNetCoreInstrumentation()
                .AddHttpClientInstrumentation()
                .AddRuntimeInstrumentation())
        .WithTracing(tracing =>
            tracing
                .AddAspNetCoreInstrumentation()
                .AddHttpClientInstrumentation());

    // AddOpenTelemetryExporters wires OTLP exporter to Aspire Dashboard locally
    builder.AddOpenTelemetryExporters();

    return builder;
}

Aspire Dashboard (http://localhost:15888) provides:

Traces:
  → Each incoming request to any service creates a trace
  → Trace spans: HTTP handler → MediatR handler → EF Core SQL → HTTP to upstream
  → End-to-end: "Nurse submits prescription → PrescriptionService → PatientService → DB"
  → See total duration, breakdown per span, errors in red

Structured Logs:
  → All service logs in one view — no switching between terminal windows
  → Filter by: service, severity (Error, Warning, Info), time range
  → Search log message content
  → Each log entry links to its trace (by traceId)

Metrics:
  → HTTP request rate, error rate per service
  → ASP.NET Core: requests/sec, response time histogram
  → Runtime: GC pressure, thread pool, memory
  → Custom business metrics (prescription approvals, INR checks)

Resources:
  → All running services, containers, and infrastructure
  → Port assignments, health status, environment variables

// ActivitySource for clinical domain tracing
// Register once per assembly
public static class ClinicalTelemetry
{
    public static readonly ActivitySource Source =
        new ActivitySource("SystemForge.Clinical.Prescriptions");
}

// In handler — add a custom span to the distributed trace
public sealed class ApprovePrescriptionHandler
    : IRequestHandler<ApprovePrescriptionCommand, Result>
{
    public async Task<Result> Handle(
        ApprovePrescriptionCommand command, CancellationToken ct)
    {
        using var activity = ClinicalTelemetry.Source.StartActivity("ApprovePrescription");
        activity?.SetTag("prescription.id",  command.PrescriptionId);
        activity?.SetTag("prescription.medication", command.MedicationName);
        activity?.SetTag("inr.value", command.InrValue);

        var prescription = await _repository.GetByIdAsync(
            PrescriptionId.Of(command.PrescriptionId), ct);

        if (prescription is null)
        {
            activity?.SetStatus(ActivityStatusCode.Error, "Prescription not found");
            return Result.Failure(Error.NotFound("Prescription", command.PrescriptionId));
        }

        var result = prescription.Approve(command.InrValue, command.CheckedAt, command.ApprovedBy);

        if (result.IsFailure)
            activity?.SetStatus(ActivityStatusCode.Error, result.Error.Message);
        else
            activity?.SetTag("prescription.status", "Approved");

        return result;
    }
}

// Register the ActivitySource with OpenTelemetry:
.WithTracing(tracing => tracing
    .AddSource("SystemForge.Clinical.Prescriptions")
    // ...other sources
)

// Clinical business metrics visible in Aspire Dashboard and production monitoring

public static class ClinicalMetrics
{
    private static readonly Meter Meter =
        new Meter("SystemForge.Clinical.Prescriptions");

    public static readonly Counter<long> PrescriptionsApproved =
        Meter.CreateCounter<long>(
            "clinical.prescriptions.approved.total",
            description: "Total Warfarin and other prescriptions approved");

    public static readonly Histogram<double> InrValueAtApproval =
        Meter.CreateHistogram<double>(
            "clinical.inr.value_at_approval",
            unit: "INR",
            description: "Distribution of INR values at prescription approval");

    public static readonly ObservableGauge<long> PendingPrescriptions =
        Meter.CreateObservableGauge<long>(
            "clinical.prescriptions.pending.count",
            () => PrescriptionCountGauge.GetPendingCount(),
            description: "Current count of prescriptions awaiting approval");
}

// In the handler, after successful approval:
ClinicalMetrics.PrescriptionsApproved.Add(1, new TagList
{
    ["medication"] = prescription.MedicationName.Value,
    ["ward_id"]    = prescription.WardId?.ToString() ?? "unassigned"
});

ClinicalMetrics.InrValueAtApproval.Record(command.InrValue, new TagList
{
    ["medication"] = prescription.MedicationName.Value,
    ["in_range"]   = (command.InrValue >= 2.0 && command.InrValue <= 3.0).ToString()
});

// Register the meter:
.WithMetrics(metrics => metrics.AddMeter("SystemForge.Clinical.Prescriptions"))

// For production: export to Azure Monitor, Jaeger, or Grafana Tempo
// Aspire Dashboard is for local development only

// Export telemetry based on environment:
private static IHostApplicationBuilder AddOpenTelemetryExporters(
    this IHostApplicationBuilder builder)
{
    var useOtlpExporter = !string.IsNullOrWhiteSpace(
        builder.Configuration["OTEL_EXPORTER_OTLP_ENDPOINT"]);

    if (useOtlpExporter)
    {
        // In production: set OTEL_EXPORTER_OTLP_ENDPOINT to your backend
        // Azure Monitor: https://ingest.monitor.azure.com/...
        // Jaeger: http://jaeger:4317
        builder.Services.AddOpenTelemetry().UseOtlpExporter();
    }

    // Azure Monitor Application Insights (alternative):
    if (!string.IsNullOrEmpty(builder.Configuration["ApplicationInsights:ConnectionString"]))
    {
        builder.Services.AddOpenTelemetry()
            .UseAzureMonitor(options =>
                options.ConnectionString =
                    builder.Configuration["ApplicationInsights:ConnectionString"]);
    }

    return builder;
}

// local.settings / appsettings.Development.json for Aspire Dashboard:
// "OTEL_EXPORTER_OTLP_ENDPOINT": "http://localhost:18889"
// (Aspire Dashboard's OTLP endpoint — automatically configured by AppHost)