System Design Interview Tips

Below are system design interview tips that aren’t always obvious. These helped me pass my job interview, and I hope they help you pass yours.

1. Take a walk before the interview to clear your mind and get your brain working.
2. Communicate with your interviewer, but don’t try to make friends with them. Focus on solving the problem.
3. If you’re interviewing for a senior role, lead the conversation. For junior roles, let the interviewer set direction.
4. Lead the conversation but don’t monologue. Pause at key points to check for questions or feedback.
5. Identify what makes your system challenging. Each system has a core puzzle. For live commenting, it’s real-time message delivery. For YouTube, it’s adaptive video serving based on device and network quality.
6. You usually don’t need back-of-the-envelope (BOE) calculations at upfront. BOE is usually needed for deep dive.
7. For BOE, use quick numbers:
   1. 1MB or 1M -> 1e6
   2. 10M -> 1e7
   3. 1 day -> 86400 sec -> close to 100,000 sec -> 1e5
   4. Example: QPS for 10M posts/day -> 1e7/1e5 = 100 posts/sec
8. Connect your system design and technical choices to the requirements.
9. Take notes. Your interviewer might not write feedback immediately and could forget something.
10. Your biggest enemy might not be your technical skills, but time management. You only get around 35 minutes, so use them wisely.
11. Practice with someone who interviews at Big Tech. You’ll get relevant evaluation and targeted feedback. I used HelloInterview for mock system design, behavioral, and coding interviews and was pleased with the experience. Use my referral link for 20% discount on your first mock interview.

Good luck!