Metrics and Alerting（指標與告警）

// Prometheus Metrics（prometheus-net）
using Prometheus;
 
// Counter
private static readonly Counter RequestCounter = Metrics.CreateCounter(
    "http_requests_total", "Total HTTP requests",
    new CounterConfiguration { LabelNames = new[] { "method", "path", "status" } });
 
// Histogram
private static readonly Histogram RequestDuration = Metrics.CreateHistogram(
    "http_request_duration_seconds", "HTTP request duration",
    new HistogramConfiguration
    {
        LabelNames = new[] { "method", "path" },
        Buckets = Histogram.LinearBuckets(0.01, 0.05, 20) // 10ms ~ 1s
    });
 
// Gauge
private static readonly Gauge ActiveConnections = Metrics.CreateGauge(
    "active_connections_total", "Current active connections");
 
// Middleware
app.Use(async (context, next) =>
{
    ActiveConnections.Inc();
    using (RequestDuration
        .WithLabels(context.Request.Method, context.Request.Path)
        .NewTimer())
    {
        await next();
    }
    RequestCounter
        .WithLabels(context.Request.Method, context.Request.Path,
                     context.Response.StatusCode.ToString())
        .Inc();
    ActiveConnections.Dec();
});
 
// 暴露 /metrics endpoint
app.MapMetrics(); // GET /metrics -> Prometheus format

// prom-client
import { Counter, Histogram, Gauge, Registry, collectDefaultMetrics } from "prom-client";
 
const register = new Registry();
collectDefaultMetrics({ register }); // Node.js 預設指標
 
const requestCounter = new Counter({
  name: "http_requests_total",
  help: "Total HTTP requests",
  labelNames: ["method", "path", "status"],
  registers: [register],
});
 
const requestDuration = new Histogram({
  name: "http_request_duration_seconds",
  help: "HTTP request duration in seconds",
  labelNames: ["method", "path"],
  buckets: [0.01, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5],
  registers: [register],
});
 
// Express middleware
app.use((req, res, next) => {
  const end = requestDuration.startTimer({ method: req.method, path: req.route?.path ?? req.path });
  res.on("finish", () => {
    end();
    requestCounter.inc({ method: req.method, path: req.route?.path ?? req.path, status: res.statusCode });
  });
  next();
});
 
// /metrics endpoint
app.get("/metrics", async (req, res) => {
  res.set("Content-Type", register.contentType);
  res.end(await register.metrics());
});

from prometheus_client import Counter, Histogram, Gauge, generate_latest
import time
 
# 定義指標
REQUEST_COUNT = Counter(
    "http_requests_total", "Total HTTP requests",
    ["method", "path", "status"]
)
REQUEST_DURATION = Histogram(
    "http_request_duration_seconds", "HTTP request duration",
    ["method", "path"],
    buckets=[0.01, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5]
)
ACTIVE_CONNECTIONS = Gauge(
    "active_connections_total", "Current active connections"
)
 
# FastAPI middleware
@app.middleware("http")
async def metrics_middleware(request, call_next):
    ACTIVE_CONNECTIONS.inc()
    start = time.time()
    response = await call_next(request)
    duration = time.time() - start
 
    REQUEST_COUNT.labels(
        method=request.method,
        path=request.url.path,
        status=response.status_code
    ).inc()
    REQUEST_DURATION.labels(
        method=request.method,
        path=request.url.path
    ).observe(duration)
    ACTIVE_CONNECTIONS.dec()
    return response
 
# /metrics endpoint
@app.get("/metrics")
def metrics():
    return Response(content=generate_latest(), media_type="text/plain")