<h2>Principles of System Design</h2>
    <p>Effective system design is the foundation of scalable applications. Whether you're building a startup or an enterprise system, understanding these core principles ensures your architecture can grow with your needs.</p>

    <h3>Scalability Fundamentals</h3>
    <p>Scalability is the ability of a system to handle increasing loads effectively:</p>
    <ul>
      <li><strong>Vertical Scaling:</strong> Increasing resources (CPU, RAM) of single servers</li>
      <li><strong>Horizontal Scaling:</strong> Adding more servers to distribute load</li>
      <li><strong>Database Scalability:</strong> Sharding, replication, and optimization</li>
      <li><strong>Elasticity:</strong> Dynamic resource allocation based on demand</li>
    </ul>

    <h3>Load Balancing Strategies</h3>
    <p>Distribute traffic efficiently across multiple servers:</p>
    <pre><code>

// Example: Round-robin load balancing const servers = ['server1', 'server2', 'server3']; let currentIndex = 0;

function getNextServer() { const server = servers[currentIndex]; currentIndex = (currentIndex + 1) % servers.length; return server; }

// Advanced: Least connections strategy function getLeastBusyServer() { return servers.reduce((prev, current) => current.connections < prev.connections ? current : prev ); } </code></pre>

    <h3>Caching Strategies</h3>
    <p>Reduce latency and database load with effective caching:</p>
    <ul>
      <li><strong>CDN Caching:</strong> Geographic distribution of static content</li>
      <li><strong>Application-Level Cache:</strong> Redis, Memcached for frequently accessed data</li>
      <li><strong>Database Query Caching:</strong> Caching expensive queries</li>
      <li><strong>HTTP Caching:</strong> Browser caching with appropriate headers</li>
    </ul>

    <h3>Database Design Patterns</h3>
    <p>Choose the right database design for your needs:</p>
    <pre><code>

// Example: Database schema design for high scalability // Users service database { users: { _id: ObjectId, email: String, profile: { name: String, avatar: String }, createdAt: Date } }