How to prepare for a system design interview

Short answer

Clarify functional and non-functional requirements first. Estimate traffic and storage, sketch a high-level design, then deep-dive into data modeling, API design, and bottlenecks. Discuss trade-offs explicitly and justify your choices.

Details

System design interviews evaluate your ability to build scalable, reliable systems collaboratively. Start by asking about scale (DAU, read/write ratio), consistency needs, and latency requirements. Propose a basic design (e.g., load balancer to app servers to database) and iterate. Address caching, CDN, database sharding, and message queues as needed.

Practice with real-world systems like URL shorteners, news feeds, or chat apps. For understanding distributed data patterns, How to design a multi-region architecture on AWS illustrates many concepts interviewers expect. If you need to brush up on networking basics, how to calculate CIDR is useful for discussing IP allocation and VPC design.

Tips

• Communicate constantly; interviewers want to see your thought process, not a perfect final diagram.
• Quantify everything with back-of-the-envelope math to show you think at scale.
• Always mention monitoring and operational concerns; design does not end at deployment.