How to prepare and ace your system design interview

Far too many candidates with deep technical expertise struggle to translate their knowledge and experience to the signals sought in a System Design or Product Architecture interview. I want to share my experience as an experienced interviewer at Meta and as a mock interviewer who has helped many prepare for their interviews and get offers.

As a former Staff Engineer at Meta and Engineering Manager at both Meta and Google, I've conducted over 300 technical interviews and gained a calibrated view of the performance that is expected to get an offer. I've also performed 150+ mock interviews on meetapro.com, giving me unique insights into how candidates can utilize their time fully leading up to the big day.

Making the Most of Your Mock Interviews

Share context with your mock interviewer

One of the most valuable aspects of mock interviews is the opportunity to identify and strengthen your weak areas. Share specific technical concepts you struggle with, allowing your interviewer to assess how you discuss tradeoffs in these areas. They can craft questions that challenge and expand your understanding and provide targeted feedback for improvement.

You should also share the companies you are interviewing with and your timeline, allowing your interviewer to focus on company-specific expectations, share insights about commonly asked questions, and prioritize areas that will have the most impact in your available prep time.

Trust the Interviewer's Question Selection

While it may be tempting to request specific questions, experienced interviewers are highly calibrated on certain problems. We know the exact hiring bar for each question, the various approaches and their implications, and different ways to progressively challenge candidates to see how far they can go.

This calibration enables your interviewer to provide accurate assessments aligning with company standards. While they might accommodate specific requests, the evaluation might be less realistic.

Avoid doing a mock with a question you're already familiar with to not create a false sense of preparedness and prevent you from identifying genuine knowledge gaps.

Start Early

Many candidates make the mistake of booking a mock interview only days before their interview. While that is useful as a warm-up (and maybe a confidence booster if you do well), you are missing an opportunity to get the most out of these mocks. By having a mock interview early in your preparation, the interviewer can help identify gaps that you can spend more time focusing on and that have an impact on how you prepare. You can always book additional sessions closer to the interview once you feel more prepared.

Essential Tips for Your Actual Interview

Component Selection Strategy

Choose components based on the non-functional requirements rather than familiarity. It's okay to select components you're less experienced with if they're the right choice. Don't be afraid to be transparent about your experience level while demonstrating sound architectural reasoning. And of course, always discuss alternatives and their tradeoffs to justify your choice.

Clear Communication and Flow

Once you have laid down the components, present your data flow clearly by walking through the user journey. Show how each component interacts in sequence. Speaking confidently and clearly is important, especially when explaining complex concepts.

As a practical tip – practice using tools like excalidraw.com. Being familiar with the tool will help you translate your thoughts into demonstrable diagrams a lot easier.

Scale Calculations

Avoid over-investing time in back-of-the-envelope calculations early on in the interview. Standard scalability principles typically apply for systems designed for billions of users, so the exact numbers are less critical. Simply acknowledge the scale requirements to the interviewer and communicate that you'll design accordingly. You can save detailed calculations for specific decision points where they truly impact architectural choices.

Don't spend too much time on basic, "high-level" designs

This advice might contradict many interview preparation materials, but I have seen way too many candidates spend more than half of their interview just on a basic design. If you know the optimized solution, you are wasting a lot of time here. This is especially true for L5+ candidates; a high-level design is not going to demonstrate the technical depth that the interviewer is looking for. Focusing on optimizations that demonstrate deeper system understanding is much more effective.