ServiceLevelIndicators.Asp 10.0.0-preview.2

ServiceLevelIndicators.Asp

ASP.NET Core middleware that automatically emits Service Level Indicator (SLI) latency metrics for every API operation. Built on the ServiceLevelIndicators core library and the standard System.Diagnostics.Metrics API.

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

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();

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);

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