How to Ace Your System Design Interview

Introduction

System design interviews are notoriously difficult. Unlike coding interviews where there is often a single "correct" optimal solution, system design interviews are open-ended discussions about trade-offs. Your goal isn't just to build a working system, but to demonstrate your ability to make architectural decisions under constraints.

The HELPS Framework

A structured approach is crucial. We recommend the HELPS framework:

• H - Requirements (Functional & Non-functional)
• E - Estimations (Traffic, Storage, Bandwidth)
• L - High-level Design (Diagramming core components)
• P - Deep Dive (Database schema, APIs, Algorithms)
• S - Scale & Bottlenecks (Caching, Sharding, Load Balancing)

1. Clarify Requirements

Never start drawing immediately. Ask questions. "Is this a chat app like WhatsApp (1-on-1) or Slack (Channels)?" "Do we need to support read receipts?" These questions show you understand product requirements affect engineering decisions.

2. Back-of-the-Envelope Calculations

You don't need exact numbers, but orders of magnitude matter. If you're designing for 100 users, a single SQL database is fine. If it's 100 million, you need sharding. Quickly estimate:

• QPS (Queries Per Second)
• Storage requirements (per day/year)
• Network bandwidth

3. Communication is Key

Treat the interviewer as a colleague. Drive the discussion, but check in frequently. "I'm thinking of using a NoSQL database here for better write throughput, does that sound reasonable to you?"

Conclusion

Practice is the only way to get comfortable with ambiguity. Use tools like EngMock.ai to simulate real interview scenarios and get AI feedback on your design choices.