Signals

Good

• Collaborate
• Work under pressure
• Resolve ambiguity constructively
• Ask good questions

Bad

• Over-engineering
• Narrow mindedness
• Stubbornness

4-Step Process

1. Understand the problem and establish the design scope (3-10 mins)

• Answering without a thorough understanding of the requirement is a huge red flag
• Ask right questions, make proper assumption, gather all the information needed to build a system, write them down.
• Example questions:
  • What features?
  • What volume? How many users?
  • How fast anticipate to scale up?
  • What’s the technology stack to leverage?

2. Propose high-level design and get buy-in (10-15 mins)

• Develop a high-level design and reach an agreement with the interviewer on the design. Collaborate with the interviewer.
  • Come up with initial blueprint. Ask for feedback.
  • Draw box diagrams with key components on whiteboard/paper.
  • Do back-of-the-envelop calculations to evaluate blueprint can scale. Think out loud.
  • (Optionally) Go through a few concrete use cases.

3. Design deep dive (10-25 mins)

At this stage, should have achieved:

• Agreed on overall goals and feature scope.
• Sketched out a high-level blueprint for overall design.
• Obtained feedback from interviewer on high-level design.
• Had some initial ideas about areas to focus on in deep dive.

4. Wrap up (3-5 mins)

Interviewer ask followup questions or discuss additional points.

• Recap of the design. Especially important if suggested a few solutions.
• Identify system bottlenecks and discuss potential improvements.
• Error cases (server failure, network loss, etc).
• Operation issues. Monitor metrics and error logs. Roll out system.
• Handle scale curve.
• Propose other refinements.

Dos and Don’ts

Dos

• Ask for clarification.
• Understand the requirement.
• Fit the scale of the business.
• Think out loud.
• Suggest multiple approaches.
• Go into details after finalize blueprint.
• Design critical part first.
• Bounce ideas off the interviewer.

Don’ts

• Be unprepared for typical questions.
• Jump into solution without clarifications.
• Go into too much details at the beginning.
• Hesitate to ask for hints if get stuck.
• Don’t think it is done until the interviewer says so.