Node.js
observability

// logger.ts import pino from 'pino'; export const logger = pino({ level: process.env.LOG_LEVEL || 'info', formatters: { level: (label) => ({ level: label }) }, timestamp: pino.stdTimeFunctions.isoTime, redact: ['req.headers.authorization', 'body.password'] // PII protection }); // app.ts — attach request logger middleware import pinoHttp from 'pino-http'; app.use(pinoHttp({ logger, customLogLevel: (req, res, err) => res.statusCode >= 500 ? 'error' : 'info', customSuccessMessage: (req, res) => `${req.method} ${req.url} ${res.statusCode}`, serializers: { req: (req) => ({ method: req.method, url: req.url, requestId: req.id }), res: (res) => ({ statusCode: res.statusCode }) } }));

import { v4 as uuid } from 'uuid'; import { AsyncLocalStorage } from 'async_hooks'; export const requestContext = new AsyncLocalStorage<{ requestId: string; userId?: string }>(); // Middleware: set/propagate correlation ID export function correlationMiddleware(req: Request, res: Response, next: NextFunction) { const requestId = (req.headers['x-request-id'] as string) || uuid(); res.setHeader('x-request-id', requestId); requestContext.run({ requestId }, () => { req.requestId = requestId; next(); }); } // Use requestId in any log from any async context: logger.info({ requestId: requestContext.getStore()?.requestId, orderId }, 'Order processed'); // Propagate to downstream HTTP calls: axios.post(serviceUrl, payload, { headers: { 'x-request-id': requestContext.getStore()?.requestId } });

// ✅ app.ts — App Insights MUST be the first import import './telemetry'; // initialise before everything else import express from 'express'; import { ordersRouter } from './routes/orders'; // ... rest of imports // telemetry.ts import appInsights from 'applicationinsights'; appInsights .setup(process.env.APPINSIGHTS_CONNECTION_STRING) .setAutoCollectRequests(true) // HTTP request tracking .setAutoCollectDependencies(true) // DB, HTTP, queue calls .setAutoCollectExceptions(true) // uncaught exceptions .setAutoCollectPerformance(true) // CPU, memory, event loop .setDistributedTracingMode(appInsights.DistributedTracingModes.AI_AND_W3C) .start(); export const client = appInsights.defaultClient;

import { client } from './telemetry'; // Track a custom business event with properties client.trackEvent({ name: 'OrderPlaced', properties: { orderId, userId, amount: total, region } }); // Track a custom metric (e.g., queue depth) client.trackMetric({ name: 'QueueDepth', value: queueDepth }); // Track an exception with context try { await processPayment(order); } catch (err) { client.trackException({ exception: err as Error, properties: { orderId, userId, operation: 'payment' } }); throw err; } // Track a dependency manually (e.g., a Redis call) const startTime = Date.now(); await redisClient.get(key); client.trackDependency({ target: 'redis', name: `GET ${key}`, data: key, duration: Date.now() - startTime, resultCode: 200, success: true, dependencyTypeName: 'Redis' });