Logging & Monitoring

Logging & Monitoring

Effective logging and monitoring are essential for maintaining, debugging, and understanding your Node.js applications in production. They help you track errors, analyze performance, detect security issues, and understand user behavior.

Why Logging Matters

Setting Up Winston Logger

Winston is the most popular logging library for Node.js:

npm install winston

Basic Winston setup:

const winston = require('winston');

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

logger.info('Server started on port 3000');
logger.warn('API rate limit exceeded', { ip: '192.168.1.1' });
logger.error('Database connection failed', { error: err.message });

Morgan HTTP Request Logging

Morgan is an HTTP request logger middleware for Express:

npm install morgan

const express = require('express');
const morgan = require('morgan');

const app = express();

app.use(morgan('combined')); // Apache combined format

// Write logs to file
const accessLogStream = fs.createWriteStream(
  path.join(__dirname, 'logs', 'access.log'),
  { flags: 'a' }
);

app.use(morgan('combined', { stream: accessLogStream }));

Health Check Endpoints

// Simple health check
app.get('/health', (req, res) => {
  res.status(200).json({ status: 'ok' });
});

// Detailed health check
app.get('/health/detailed', async (req, res) => {
  const health = {
    uptime: process.uptime(),
    timestamp: Date.now(),
    status: 'ok',
    checks: {
      database: mongoose.connection.readyState === 1 ? 'up' : 'down',
      redis: await redisClient.ping() ? 'up' : 'down'
    }
  };

  res.status(200).json(health);
});