System Design Interview Cheat Sheet: Core Concepts and Trade-offs

Introduction to System Design Fundamentals

System design interviews often assess a candidate's ability to think critically about large-scale distributed systems. This cheat sheet provides a structured overview of common concepts, helping to build a solid foundation. Understanding these fundamentals is crucial for designing scalable, reliable, and performant systems.

Key System Components and Considerations

• Load Balancers: Distribute incoming network traffic across multiple servers to improve responsiveness and availability.
• Caching: Store frequently accessed data closer to the user or in faster memory to reduce latency and database load.
• Databases: SQL vs. NoSQL considerations, horizontal vs. vertical scaling, CAP theorem implications.
• Message Queues: Decouple services, buffer requests, and handle asynchronous processing for resilience and scalability.
• Distributed Systems Concepts: Consistency models, fault tolerance, consensus algorithms (e.g., Paxos, Raft).
• APIs: REST, GraphQL, gRPC design principles and trade-offs.

Scalability and Performance Metrics

Understanding basic numbers and metrics is vital for back-of-the-envelope calculations during system design. These include latency figures for various operations (e.g., memory access, disk I/O, network round trips) and throughput expectations. Concepts like QPS (Queries Per Second) and latency are critical for capacity planning.

Architectural Trade-offs

System design is fundamentally about making trade-offs. Decisions often involve balancing consistency vs. availability (CAP theorem), performance vs. cost, complexity vs. maintainability, and strong consistency vs. eventual consistency. Recognizing these trade-offs and articulating their impact is a hallmark of good system design.