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System Design

Design scalable, reliable distributed systems. Structure your approach, communicate trade-offs, and show senior-level thinking.

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Interview framework

1

Clarify requirements

Functional requirements (what it does) and non-functional requirements (scale, latency, availability, consistency).
2

Estimate scale

DAU, requests/second, data volume, read/write ratio. Back-of-envelope math matters.
3

High-level design

Core components: clients, load balancers, app servers, databases, caches.
4

Deep dive

Focus on the most critical or technically interesting component.
5

Identify bottlenecks

Single points of failure, hot spots, scaling limits.

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Topics

Scalability

Horizontal vs vertical scaling, load balancers, CDN.

Caching

Cache-aside, write-through, eviction policies, Redis.

Databases

SQL vs NoSQL, sharding, replication, CAP theorem.

Message Queues

Kafka, pub/sub, event-driven architecture.
◆ Trade-offs Over Answers
System design interviews have no single correct answer. What interviewers evaluate is your ability to identify trade-offs, justify decisions, and adapt when requirements change.
💡 Interview Tip
Always ask about the scale before designing. A system serving 1,000 users and one serving 100 million users require completely different architectures. Never assume.