name: observability-setup description: Implements comprehensive observability with OpenTelemetry tracing, Prometheus metrics, and structured logging. Includes instrumentation plans, sample dashboards, and alert candidates. Use for "observability", "monitoring", "tracing", or "metrics".

Observability Setup

Implement the three pillars: Traces, Metrics, and Logs.

OpenTelemetry Tracing

// tracing.ts
import { NodeTracerProvider } from "@opentelemetry/sdk-trace-node";
import { Resource } from "@opentelemetry/resources";
import { SemanticResourceAttributes } from "@opentelemetry/semantic-conventions";
import { registerInstrumentations } from "@opentelemetry/instrumentation";
import { HttpInstrumentation } from "@opentelemetry/instrumentation-http";
import { ExpressInstrumentation } from "@opentelemetry/instrumentation-express";
import { PrismaInstrumentation } from "@prisma/instrumentation";

const provider = new NodeTracerProvider({
  resource: new Resource({
    [SemanticResourceAttributes.SERVICE_NAME]: "my-api",
    [SemanticResourceAttributes.SERVICE_VERSION]: "1.0.0",
  }),
});

registerInstrumentations({
  instrumentations: [
    new HttpInstrumentation(),
    new ExpressInstrumentation(),
    new PrismaInstrumentation(),
  ],
});

provider.register();

// Custom spans
import { trace } from "@opentelemetry/api";

const tracer = trace.getTracer("my-app");

async function processOrder(orderId: string) {
  const span = tracer.startSpan("processOrder");
  span.setAttribute("order.id", orderId);

  try {
    await validateOrder(orderId);
    await chargePayment(orderId);
    await fulfillOrder(orderId);
    span.setStatus({ code: 0 }); // OK
  } catch (error) {
    span.setStatus({ code: 2, message: error.message }); // ERROR
    throw error;
  } finally {
    span.end();
  }
}

Prometheus Metrics

// metrics.ts
import { Registry, Counter, Histogram, Gauge } from "prom-client";

const register = new Registry();

// HTTP request counter
export const httpRequestCounter = new Counter({
  name: "http_requests_total",
  help: "Total HTTP requests",
  labelNames: ["method", "route", "status_code"],
  registers: [register],
});

// HTTP request duration
export const httpRequestDuration = new Histogram({
  name: "http_request_duration_seconds",
  help: "HTTP request duration in seconds",
  labelNames: ["method", "route", "status_code"],
  buckets: [0.1, 0.5, 1, 2, 5, 10],
  registers: [register],
});

// Active connections
export const activeConnections = new Gauge({
  name: "active_connections",
  help: "Number of active connections",
  registers: [register],
});

// Business metrics
export const ordersProcessed = new Counter({
  name: "orders_processed_total",
  help: "Total orders processed",
  labelNames: ["status"],
  registers: [register],
});

// Middleware
app.use((req, res, next) => {
  const start = Date.now();

  res.on("finish", () => {
    const duration = (Date.now() - start) / 1000;
    const route = req.route?.path || "unknown";

    httpRequestCounter.inc({
      method: req.method,
      route,
      status_code: res.statusCode,
    });

    httpRequestDuration.observe(
      { method: req.method, route, status_code: res.statusCode },
      duration
    );
  });

  next();
});

// Metrics endpoint
app.get("/metrics", async (req, res) => {
  res.set("Content-Type", register.contentType);
  res.end(await register.metrics());
});

Structured Logging

// logger.ts
import pino from "pino";

export const logger = pino({
  level: process.env.LOG_LEVEL || "info",
  formatters: {
    level: (label) => ({ level: label }),
  },
  base: {
    service: "my-api",
    environment: process.env.NODE_ENV,
  },
});

// Usage
logger.info({ userId: "123", action: "login" }, "User logged in");
logger.error({ err: error, orderId: "456" }, "Order processing failed");

Sample Dashboard (Grafana)

{
  "dashboard": {
    "title": "API Overview",
    "panels": [
      {
        "title": "Request Rate",
        "targets": [{
          "expr": "rate(http_requests_total[5m])"
        }]
      },
      {
        "title": "Error Rate",
        "targets": [{
          "expr": "rate(http_requests_total{status_code=~"5.."}[5m])"
        }]
      },
      {
        "title": "p95 Latency",
        "targets": [{
          "expr": "histogram_quantile(0.95, rate(http_request_duration_seconds_bucket[5m]))"
        }]
      },
      {
        "title": "Active Connections",
        "targets": [{
          "expr": "active_connections"
        }]
      }
    ]
  }
}

Alert Candidates

# alerts.yml
groups:
  - name: api_alerts
    interval: 30s
    rules:
      - alert: HighErrorRate
        expr: rate(http_requests_total{status_code=~"5.."}[5m]) > 0.05
        for: 5m
        labels:
          severity: critical
        annotations:
          summary: "High error rate detected"

      - alert: HighLatency
        expr: histogram_quantile(0.95, rate(http_request_duration_seconds_bucket[5m])) > 2
        for: 10m
        labels:
          severity: warning
        annotations:
          summary: "p95 latency above 2s"

      - alert: LowAvailability
        expr: rate(http_requests_total{status_code="200"}[5m]) / rate(http_requests_total[5m]) < 0.95
        for: 5m
        labels:
          severity: critical
        annotations:
          summary: "Availability below 95%"

Output Checklist

• OpenTelemetry tracing configured
• Prometheus metrics instrumented
• Structured logging implemented
• Sample dashboards created
• Alert rules defined
• Metrics endpoint exposed
• Instrumentation tested ENDFILE