{"id":1271,"date":"2026-07-11T23:49:53","date_gmt":"2026-07-11T18:19:53","guid":{"rendered":"https:\/\/lastroundai.com\/blog\/?post_type=iq&p=1271"},"modified":"2026-07-19T09:23:29","modified_gmt":"2026-07-19T03:53:29","slug":"system-design","status":"publish","type":"iq","link":"https:\/\/lastroundai.com\/interview-questions\/system-design","title":{"rendered":"System Design Interview Questions (2026): Must-Know Q&A"},"content":{"rendered":"

Eric Brewer sketched what became the CAP theorem as a conjecture during a keynote at the 2000 ACM Symposium on Principles of Distributed Computing. He didn’t prove it. Two years later, MIT researchers Seth Gilbert and Nancy Lynch did, formalizing consistency, availability, and partition tolerance into an actual theorem and showing mathematically that you can’t guarantee all three once a network partition happens (Gilbert and Lynch, ACM SIGACT News, 2002<\/a>). Most candidates can recite “CAP” on demand. Fewer can explain what “partition tolerance” formally means, or why the real decision in a 2026 interview almost never comes down to choosing C over A, it comes down to how much staleness one specific feature can tolerate before it breaks something a user actually notices.<\/p>\n

Here’s an opinion that might be wrong: I think most system design prep spends too much time on box-and-arrow diagrams and not nearly enough on what happens when one of those boxes goes down at 2am. You can draw a clean architecture for a URL shortener and still lose the round if you freeze the moment an interviewer asks what happens when your database’s primary node dies mid-write. Drawing boxes is the easy 60 percent of a system design interview. Failure modes, data models, and trade-offs are the other 40, and that’s usually the part that decides whether the offer is senior or mid-level.<\/p>\n

This page covers system design interview questions across nine areas: scalability and the latency-versus-throughput split, load balancing, caching, databases (SQL vs NoSQL, indexing, sharding, replication), the CAP theorem and consistency models, message queues, rate limiting, API design, and five worked “design X” scenarios you’re actually likely to get asked, a URL shortener, a news feed, a chat app, a rate limiter, and a notification system. If you want a minute-by-minute framework for running a live 45-minute design round instead of a question bank, LastRoundAI’s system design interview guide<\/a> covers that separately. This page answers the “what will they actually ask” question. That one answers the “how do I structure my 45 minutes” question.<\/p>\n

55<\/span>Questions<\/span><\/div>
Trade-offs Over Diagrams<\/span>Core Topic<\/span><\/div>
Whiteboard + Verbal<\/span>Format<\/span><\/div>
2002<\/span>CAP Proof Year<\/span><\/div><\/div>\n

Scalability, latency, and throughput: the fundamentals interviewers check first<\/h2>\n

Every loop opens here, senior or junior. Get this section wrong and the interviewer recalibrates downward for the rest of the round, whether they say so or not.<\/p>\n

<\/span>Easy questions<\/h2>16<\/span><\/div>
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