System Design Interview Masterclass: Components, Patterns and Practice
An interactive guide to the system design round used by large US technology employers. The page walks through the building blocks of a distributed system — load balancers, CDNs, databases, caches, message queues, API gateways, object storage and microservices — along with the trade-offs each one carries, then lets you size infrastructure against a user-count slider, compare architecture patterns, and work through practice prompts such as designing a URL shortener, WhatsApp, YouTube or Uber.
Core system components and their trade-offs
The component explorer covers load balancers, CDNs, databases, caches, message queues, API gateways, object storage and microservices. Each entry lists common implementations, the metrics interviewers tend to probe, and an explicit pros-and-cons list — because naming a component is worth little unless you can also state what it costs you in complexity, consistency or latency.
Architecture patterns and when each one fits
Monolithic, microservices, serverless, event-driven and CQRS architectures are compared on what they are, the scale they suit, their complexity, and the situations where each is the right call. The recurring point is that a monolith remains the correct answer for a small team or an early product, and that distribution buys scale at the price of operational overhead.
Practice prompts and infrastructure sizing
Four classic interview prompts — a URL shortener, WhatsApp, YouTube and Uber — each come with stated requirements, suggested components, and hints you can reveal one at a time. A slider-driven calculator estimates queries per second, storage, server count, cache size and bandwidth from a target user base, illustrating how infrastructure needs change as scale grows.
Scaling, reliability, performance and security
A reference section groups the vocabulary interviewers expect: horizontal versus vertical scaling, sharding and read replicas; redundancy, failover, health checks and circuit breakers; caching strategies, connection pooling, lazy loading and compression; and authentication, rate limiting, encryption and API security. Recommended books and engineering resources are listed alongside.