You can build distributed systems at work, yet when an interviewer says "design a notification service" the words dry up. You draw a load balancer, mutter something about caching, and watch the interviewer's face stay politely blank. The problem is not knowledge. It is that you have never practised explaining trade-offs out loud, under a clock, to someone whose job is to push back.
System Design Interviews by Doing fixes that with twelve hands-on labs. Instead of memorising diagrams, you build small working versions of the components interviewers ask about, measure how they behave, break them on purpose and then rehearse describing what you saw. Every chapter ends with a timed exercise that mimics the real conversation.
You will build and defend: a requirements and estimation routine that fits in five minutes; API contracts that survive versioning questions; a stateless service behind a load balancer with health checks; a cache with real invalidation bugs you can reproduce; a comparison of relational and distributed storage on the same workload; a message queue with at-least-once delivery and idempotent consumers; a replicated store you partition by hand to watch consistency guarantees change; a multi-region failover plan; an observability layer with a cost model; and a whiteboard narration technique that keeps interviewers nodding.
Three capstone projects give you full forty-five-minute rehearsals: a URL shortener under strict latency and availability targets, a notification platform with retries and dead-letter handling, and a real-time collaborative editor you must defend against hostile follow-up questions.
Everything runs on a laptop with Python, Docker and a terminal. No cloud account is required.
This book is for mid-level and senior engineers interviewing at companies that run system design rounds, for engineers moving from one specialism into backend or platform roles, and for anyone who understands the pieces but has never had to argue for them in real time. If you want to walk into the room with reasoning you have tested rather than slides you have memorised, start here.
