Metrics.Client

Lightweight Prometheus metrics for ASP.NET Core services. Auto-collects HTTP request duration, request count, and active requests with low-cardinality labels.

Quick Start

using Metrics.Client.Extensions;

var builder = WebApplication.CreateBuilder(args);

// Add Prometheus metrics
builder.AddPrometheusMetrics(opts => opts.ServiceName = "MyService");

var app = builder.Build();

// Use Prometheus metrics middleware + /metrics endpoint
app.UsePrometheusMetrics();

await app.RunAsync();

Metrics Collected

Metric	Type	Labels	Description
http_requests_total	Counter	service, method, endpoint, status_code	Total HTTP requests processed
http_request_duration_seconds	Histogram	service, method, endpoint, status_code	Request duration in seconds
http_requests_in_flight	Gauge	service	Currently processing requests
canary_http_requests_total	Counter	service, method, status_code	HTTP requests tagged as in-cluster E2E canary traffic

Canary traffic

canary_http_requests_total is a separate, low-cardinality counter for in-cluster E2E canary traffic (the X-Canary-Run-Id header + superUser JWT flow from Canary.AspNetCore). It is incremented only when the request was auth-validated as canary (ICanaryRunContext.IsCanary == true) — never on mere header presence.

It is deliberately a separate series rather than a canary label on http_requests_total (which would double that metric's series count), and deliberately omits the endpoint label to keep cardinality minimal.

This powers a Grafana "Canary Activity" dashboard and lets SLO dashboards default-exclude canary noise, e.g.:

# Real (non-canary) request rate per service
sum by (service) (rate(http_requests_total[5m]))
  - sum by (service) (rate(canary_http_requests_total[5m]))

Consuming services pick this up automatically — no wiring change is needed beyond the existing UsePrometheusMetrics() call, provided UseCanaryAuth() is registered after it (the standard pipeline order).

Configuration

Via appsettings.json:

{
  "Metrics": {
    "ServiceName": "MyService",
    "Enabled": true,
    "MetricsPath": "/metrics"
  }
}

Or programmatically:

builder.AddPrometheusMetrics(opts =>
{
    opts.ServiceName = "MyService";
    opts.Enabled = true;
});

Prometheus Scrape Config

scrape_configs:
  - job_name: 'my-service'
    static_configs:
      - targets: ['my-service:8080']
    metrics_path: /metrics

Design Decisions

• Low cardinality: Uses route templates (not raw paths) for endpoint labels
• Health/metrics excluded: Health check and metrics endpoints are not tracked to avoid noise
• Lightweight: No-op overhead when requests hit excluded paths