Advanced Node.js

Chapter 14: Monitoring and Debugging

14.1 Application Monitoring

Monitoring helps track application health, performance, and errors in production.

// PM2 monitoring
// npm install -g pm2
// pm2 start app.js
// pm2 monit
// pm2 logs

// Application metrics
const prometheus = require('prom-client');

const httpRequestDuration = new prometheus.Histogram({
    name: 'http_request_duration_seconds',
    help: 'Duration of HTTP requests in seconds',
    labelNames: ['method', 'route', 'status_code']
});

app.use((req, res, next) => {
    const start = Date.now();
    res.on('finish', () => {
        const duration = (Date.now() - start) / 1000;
        httpRequestDuration.observe({
            method: req.method,
            route: req.route?.path || req.path,
            status_code: res.statusCode
        }, duration);
    });
    next();
});

14.2 Health Checks

// Health check endpoint
app.get('/health', async (req, res) => {
    const health = {
        uptime: process.uptime(),
        message: 'OK',
        timestamp: Date.now(),
        database: await checkDatabase(),
        redis: await checkRedis()
    };
    
    const statusCode = health.database && health.redis ? 200 : 503;
    res.status(statusCode).json(health);
});

14.3 Error Tracking

// Sentry integration
const Sentry = require('@sentry/node');

Sentry.init({
    dsn: process.env.SENTRY_DSN,
    environment: process.env.NODE_ENV
});

// Capture exceptions
try {
    riskyOperation();
} catch (error) {
    Sentry.captureException(error);
}

14.4 Debugging

// Node.js inspector
// node --inspect app.js
// Open chrome://inspect

// Debug logging
const debug = require('debug')('app:server');
debug('Server starting on port %d', port);

// Enable: DEBUG=app:* node app.js