Building Scalable APIs with Node.js

APIs are the backbone of modern applications. Here's how I approach building APIs that can scale from thousands to millions of requests.

Architecture Principles

When designing scalable APIs, I follow these core principles:

• Stateless design - Each request contains all necessary information
• Horizontal scaling - Add more servers instead of bigger servers
• Caching strategies - Reduce database load with smart caching
• Rate limiting - Protect your API from abuse

Performance Optimization

Here are the techniques that have made the biggest impact:

1. Database Query Optimization

// Bad: N+1 query problem
const users = await User.findAll();
for (const user of users) {
  user.posts = await Post.findByUserId(user.id);
}

// Good: Use joins or eager loading
const users = await User.findAll({
  include: [{ model: Post }]
});

2. Implement Proper Caching

• Redis for session data and frequently accessed objects
• CDN for static assets and API responses
• Application-level caching for computed results

3. Use Connection Pooling

const pool = new Pool({
  connectionString: process.env.DATABASE_URL,
  max: 20, // Maximum connections
  idleTimeoutMillis: 30000,
  connectionTimeoutMillis: 2000,
});

Monitoring and Observability

You can't improve what you don't measure:

• Response times - Track P50, P95, and P99 percentiles
• Error rates - Monitor 4xx and 5xx responses
• Throughput - Requests per second under load
• Resource usage - CPU, memory, and database connections

Error Handling

Proper error handling is crucial for API reliability:

app.use((err, req, res, next) => {
  logger.error('API Error:', {
    error: err.message,
    stack: err.stack,
    url: req.url,
    method: req.method
  });
  
  res.status(err.status || 500).json({
    error: process.env.NODE_ENV === 'production' 
      ? 'Internal Server Error' 
      : err.message
  });
});

Security Best Practices

• Input validation on all endpoints
• Rate limiting to prevent abuse
• Authentication and authorization for protected routes
• HTTPS everywhere - no exceptions

Testing Strategy

I use a multi-layer testing approach:

1. Unit tests for business logic
2. Integration tests for database interactions
3. Load tests to verify performance requirements
4. Contract tests to ensure API compatibility

Building scalable APIs is both an art and a science. Start with solid fundamentals, measure everything, and optimize based on real data, not assumptions.