System design is the process of defining the architecture, components, modules, interfaces, and data for a system to satisfy specified requirements. Whether preparing for senior technical interviews or designing enterprise cloud platforms, understanding scalability building blocks is essential.
1. Vertical Scaling vs. Horizontal Scaling
Vertical Scaling (Scale Up)
Adding more CPU cores, RAM, or SSD storage to a single server machine. Hard hardware limit and creates single point of failure (SPOF).
Horizontal Scaling (Scale Out)
Adding more server instances behind a load balancer. Infinite scaling potential and high fault tolerance.
2. Load Balancing Strategies
Load balancers (e.g., NGINX, HAProxy, AWS ALB) distribute incoming network traffic across multiple backend servers using algorithms:
- Round Robin: Distributes requests sequentially across servers.
- Least Connections: Routes traffic to the server with fewest active connections.
- IP Hash: Hashes client IP to ensure session stickiness to a specific server.
3. High-Speed In-Memory Caching (Redis / Memcached)
Caching stores frequently requested database records in RAM, drastically reducing DB read latency from ~50ms down to ~1ms.
Cache-Aside Pattern (Lazy Loading):
- Application checks Redis cache for requested key.
- If Cache Hit: Return data immediately to user.
- If Cache Miss: Read record from PostgreSQL database, save record to Redis cache with TTL (Time To Live), and return data.
4. Asynchronous Messaging Queues (Kafka / RabbitMQ)
De-couple heavy long-running background tasks (e.g., sending email notifications, processing video uploads, generating PDF invoices) using message queues so API endpoints respond immediately.
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