ServiceLevelIndicators.Asp 10.0.0-preview.6

ServiceLevelIndicators.Asp

ASP.NET Core middleware that automatically emits Service Level Indicator (SLI) latency metrics in milliseconds for every API operation. Built on the ServiceLevelIndicators core library, it helps teams move from generic request timing to service-specific latency metrics with dimensions such as operation, customer, location, and status.

For API versioning support, add ServiceLevelIndicators.Asp.ApiVersioning.

When To Use This Package

Choose ServiceLevelIndicators.Asp when you are building an ASP.NET Core application and want SLI metrics emitted automatically for MVC controllers or Minimal API endpoints.

Use ServiceLevelIndicators if you only need manual measurement in non-HTTP code. Add ServiceLevelIndicators.Asp.ApiVersioning when your ASP.NET Core app uses Asp.Versioning and you want the resolved API version emitted as a metric dimension.

Installation

dotnet add package ServiceLevelIndicators.Asp

Quick Start — MVC Controllers

// 1. Register with OpenTelemetry
builder.Services.AddOpenTelemetry()
    .WithMetrics(metrics =>
    {
        metrics.AddServiceLevelIndicatorInstrumentation();
        metrics.AddOtlpExporter();
    });

// 2. Configure SLI — AddMvc() enables attribute-based overrides
builder.Services.AddServiceLevelIndicator(options =>
{
    options.LocationId = ServiceLevelIndicator.CreateLocationId("public", "westus3");
})
.AddMvc();

// 3. Add the middleware
app.UseServiceLevelIndicator();

Quick Start — Minimal APIs

builder.Services.AddServiceLevelIndicator(options =>
{
    options.LocationId = ServiceLevelIndicator.CreateLocationId("public", "westus3");
});

app.UseServiceLevelIndicator();

// Mark individual endpoints
app.MapGet("/hello", () => "Hello World!")
    .AddServiceLevelIndicator();

If you configure a custom Meter in ServiceLevelIndicatorOptions, register that same meter with OpenTelemetry by calling AddServiceLevelIndicatorInstrumentation(meter).

Emitted Metrics

A meter named ServiceLevelIndicator with instrument operation.duration (milliseconds) is emitted with the following attributes:

Customizations

Add HTTP method as a dimension

builder.Services.AddServiceLevelIndicator(options => { /* ... */ })
    .AddMvc()
    .AddHttpMethod();

Enrich with custom data

Use Enrich (or EnrichAsync) to set CustomerResourceId or add custom attributes:

builder.Services.AddServiceLevelIndicator(options => { /* ... */ })
    .AddMvc()
    .Enrich(context =>
    {
        var upn = context.HttpContext.User.Claims
            .FirstOrDefault(c => c.Type == "upn")?.Value ?? "Unknown";
        context.SetCustomerResourceId(upn);
        context.AddAttribute("UserPrincipalName", upn);
    });

Override the operation name

[HttpGet("MyAction")]
[ServiceLevelIndicator(Operation = "MyCustomName")]
public IActionResult Get() => Ok();

Set CustomerResourceId from a route parameter

[HttpGet("get-by-zip-code/{zipCode}")]
public IActionResult GetByZipcode([CustomerResourceId] string zipCode) => Ok();

Or imperatively:

HttpContext.GetMeasuredOperation().CustomerResourceId = customerResourceId;

Add custom attributes from route parameters

Parameters decorated with [Measure] are automatically added as metric dimensions:

[HttpGet("name/{first}/{surname}")]
public IActionResult Get([Measure] string first, [CustomerResourceId] string surname) => Ok();

Add custom attributes manually

HttpContext.GetMeasuredOperation().AddAttribute("CustomKey", value);

// Safe version for middleware (won't throw if SLI is not configured for the route)
if (HttpContext.TryGetMeasuredOperation(out var op))
    op.AddAttribute("CustomKey", value);

Cardinality Guidance

Use CustomerResourceId, [Measure], and custom attributes for stable service dimensions such as tenant, subscription, region, or API flavor. Avoid unbounded values like request IDs, email addresses, timestamps, or arbitrary user input unless you explicitly want high-cardinality metrics and your backend can absorb the cost.

Opt-in mode

To disable automatic SLI emission on all controllers:

options.AutomaticallyEmitted = false;

Then add [ServiceLevelIndicator] only to the controllers you want measured.

Further Reading

• Full documentation and samples
• Package selection and usage reference