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