When a user reports "the site is slow", you need data, not guesses. OpenTelemetry is the open standard for collecting traces, metrics and logs, and .NET supports it natively.

Basic configuration

builder.Services.AddOpenTelemetry()
    .ConfigureResource(r => r.AddService("shop-api"))
    .WithTracing(t => t
        .AddAspNetCoreInstrumentation()
        .AddHttpClientInstrumentation())
    .WithMetrics(m => m
        .AddAspNetCoreInstrumentation()
        .AddHttpClientInstrumentation()
        .AddRuntimeInstrumentation())
    .UseOtlpExporter();

Data is sent over the OTLP protocol to any compatible system: open-source solutions, cloud services or the Aspire dashboard during development.

Custom traces

public static class Telemetry
{
    public static readonly ActivitySource Source = new("Shop.Orders");
}

using var activity = Telemetry.Source.StartActivity("ComputeShipping");
activity?.SetTag("order.country", order.Country);

Health checks

A health endpoint tells load balancers, orchestrators and monitoring systems whether the instance is ready to receive traffic.

builder.Services.AddHealthChecks()
    .AddCheck("disk-space", () =>
    {
        var free = new DriveInfo(AppContext.BaseDirectory).AvailableFreeSpace;
        return free > 500_000_000
            ? HealthCheckResult.Healthy()
            : HealthCheckResult.Degraded("Disk space running low");
    });

app.MapHealthChecks("/health");

What to really measure

Response times per endpoint, error rate, duration of queries and external calls. A few well-chosen indicators, with sensible alert thresholds, are worth more than a hundred charts nobody looks at.