Chapter 8: The Interview Day & Tips

Whiteboarding Strategies

The whiteboard (or shared doc) is your stage.

1. Step 1: Clarify Requirements (5-10 mins)

   • Don’t start drawing yet!
   • Ask: “What is the scale (DAU/MAU)?” “Read-heavy or Write-heavy?” “Mobile app or Web?”
   • Define the MVP scope: “For this 45 mins, I’ll focus on the Feed generation, not the Chat feature.”

2. Step 2: High Level Design (5-10 mins)

   • Draw the “Standard Boxes”: Client -> Load Balancer -> API Gateway -> Service -> Database.
   • Get a “Check-in”: “Does this high-level flow look good to you?”

3. Step 3: Drill Down (20 mins)

   • Identify the Bottleneck. “Since we have 10M writes/second, a single SQL DB won’t work.”
   • Propose the solution: “I’ll shard the DB by UserID” or “I’ll introduce a Write-Behind Cache.”
   • Discuss the Database Schema.

4. Step 4: Wrap Up (5 mins)

   • Mention what you missed. “If I had more time, I’d add Monitoring (Prometheus) and Distributed Tracing.”

Communication Tips

• Breadth first, then Depth: Give an overview before diving into the weeds.
• Check in often: “Does that make sense?” “Should I go deeper into the caching strategy?”
• Frameworks: Use frameworks like Five Pillars of AWS Well-Architected Framework (Operational Excellence, Security, Reliability, Performance Efficiency, Cost Optimization) to structure your answers.

Critical Advice

1. Admit what you don’t know: “I haven’t used GraphQL in production, but based on my REST experience, I assume the caching challenges would be X…” -> This shows intelligence and honesty.
2. Focus on Trade-offs: Never say “Redis is the best.” Say “Redis is great for speed, but memcached might be simpler if we don’t need persistent structures.”
3. Think Big, Start Small: Design for the end state (10M users), but explain how you launch MVP (1k users) without over-engineering.

Final Checklist

• [ ] Do you know your “War Stories” by heart?
• [ ] Can you draw a Load Balancer and describe Layer 4 vs Layer 7?
• [ ] Can you explain “CAP Theorem” in 30 seconds?
• [ ] Have you researched the company’s tech stack?

Good luck. You got this.