logging-best-practices

# Logging Best Practices Implement secure, structured logging with proper levels and context. ## Log Levels | Level | Use For | Production | |-------|---------|------------| | DEBUG | Detailed debugging | Off | | INFO | Normal operations | On | | WARN | Potential issues | On | | ERROR | Errors with recovery | On | | FATAL | Critical failures | On | ## Structured Logging (Winston) ```javascript const winston = require('winston'); const logger = winston.createLogger({ level: process.env.LOG_LEVEL || 'info', format: winston.format.combine( winston.format.timestamp(), winston.format.json() ), defaultMeta: { service: 'api-service' }, transports: [ new winston.transports.Console(), new winston.transports.File({ filename: 'error.log', level: 'error' }) ] }); // Usage logger.info('User logged in', { userId: '123', ip: '192.168.1.1' }); logger.error('Payment failed', { error: err.message, orderId: '456' }); ``` ## Request Context ```javascript const { AsyncLocalStorage } = require('async_hooks'); const storage = new AsyncLocalStorage(); app.use((req, res, next) => { const context = { requestId: req.headers['x-request-id'] || uuid(), userId: req.user?.id }; storage.run(context, next); }); function log(level, message, meta = {}) { const context = storage.getStore() || {}; logger.log(level, message, { ...context, ...meta }); } ``` ## PII Sanitization ```javascript const sensitiveFields = ['password', 'ssn', 'creditCard', 'token']...