Logging with Winston and Morgan

Good logging is essential for debugging and monitoring. Console.log won't cut it in production.

Setup

npm install winston morgan

Winston - Application Logs

const winston = require('winston');

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

// Add console in development
if (process.env.NODE_ENV !== 'production') {
  logger.add(new winston.transports.Console({
    format: winston.format.simple()
  }));
}

module.exports = logger;

Log Levels

logger.error('Database connection failed');
logger.warn('Deprecated API called');
logger.info('User logged in');
logger.http('GET /api/users');
logger.debug('Processing data...');

Custom Format

const logger = winston.createLogger({
  format: winston.format.combine(
    winston.format.timestamp({ format: 'YYYY-MM-DD HH:mm:ss' }),
    winston.format.printf(({ timestamp, level, message, ...meta }) => {
      return `${timestamp} [${level.toUpperCase()}]: ${message} ${Object.keys(meta).length ? JSON.stringify(meta) : ''}`;
    })
  ),
  transports: [
    new winston.transports.Console()
  ]
});

logger.info('User created', { userId: 1, email: 'alice@example.com' });
// 2024-01-15 10:30:00 [INFO]: User created {"userId":1,"email":"alice@example.com"}

Morgan - HTTP Request Logs

const morgan = require('morgan');

// Predefined formats
app.use(morgan('dev'));       // :method :url :status :response-time ms
app.use(morgan('combined'));  // Apache combined format
app.use(morgan('tiny'));      // Minimal output

// Custom format
app.use(morgan(':method :url :status :response-time ms - :res[content-length]'));

Morgan + Winston Integration

const morgan = require('morgan');
const logger = require('./logger');

// Create stream for winston
const stream = {
  write: (message) => logger.http(message.trim())
};

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

Skip Logging for Health Checks

app.use(morgan('combined', {
  skip: (req, res) => req.url === '/health'
}));

Daily Rotate File

npm install winston-daily-rotate-file

require('winston-daily-rotate-file');

const logger = winston.createLogger({
  transports: [
    new winston.transports.DailyRotateFile({
      filename: 'logs/app-%DATE%.log',
      datePattern: 'YYYY-MM-DD',
      maxSize: '20m',
      maxFiles: '14d'  // Keep 14 days of logs
    })
  ]
});

Complete Logger Setup

// logger.js
const winston = require('winston');
require('winston-daily-rotate-file');

const levels = {
  error: 0,
  warn: 1,
  info: 2,
  http: 3,
  debug: 4
};

const logger = winston.createLogger({
  level: process.env.LOG_LEVEL || 'info',
  levels,
  format: winston.format.combine(
    winston.format.timestamp(),
    winston.format.errors({ stack: true }),
    winston.format.json()
  ),
  defaultMeta: { service: 'my-app' },
  transports: [
    new winston.transports.DailyRotateFile({
      filename: 'logs/error-%DATE%.log',
      datePattern: 'YYYY-MM-DD',
      level: 'error',
      maxFiles: '30d'
    }),
    new winston.transports.DailyRotateFile({
      filename: 'logs/combined-%DATE%.log',
      datePattern: 'YYYY-MM-DD',
      maxFiles: '14d'
    })
  ]
});

if (process.env.NODE_ENV !== 'production') {
  logger.add(new winston.transports.Console({
    format: winston.format.combine(
      winston.format.colorize(),
      winston.format.simple()
    )
  }));
}

module.exports = logger;

Usage in Application

const logger = require('./logger');

// In route handlers
app.post('/api/users', async (req, res) => {
  try {
    const user = await User.create(req.body);
    logger.info('User created', { userId: user.id });
    res.status(201).json(user);
  } catch (error) {
    logger.error('Failed to create user', { error: error.message, stack: error.stack });
    res.status(500).json({ error: 'Internal error' });
  }
});

Key Takeaway

Use Winston for application logs and Morgan for HTTP requests. Set up daily rotation to manage log files. Include timestamps and structured metadata. Different log levels help filter what's important. Good logging saves hours of debugging.