Databases, Testing, and DeploymentLesson 6.4

Logging and monitoring Node.js applications in production

winston setup, log levels, structured JSON logging, morgan integration, correlation IDs, error logging, health check endpoints

console.log Is Not Production Logging

Production logs need levels (error/warn/info/debug), structured JSON output for log aggregators, and multiple transports.

npm install winston

const winston = require('winston');

const logger = winston.createLogger({
  level: process.env.LOG_LEVEL || 'info',
  format: winston.format.combine(
    winston.format.timestamp(),
    winston.format.json()
  ),
  transports: [
    new winston.transports.Console(),
    new winston.transports.File({ filename: 'logs/error.log', level: 'error' }),
    new winston.transports.File({ filename: 'logs/combined.log' })
  ]
});

module.exports = logger;

logger.info('Server started', { port: 3000 });
logger.error('DB connection failed', { error: err.message, stack: err.stack });

Health Check Endpoint

app.get('/health', async (req, res) => {
  const db = await checkDatabase().catch(() => false);
  res.status(db ? 200 : 503).json({
    status: db ? 'healthy' : 'degraded',
    uptime: process.uptime(),
    timestamp: new Date().toISOString()
  });
});