🧭 Interview Framework — System Design Reference

Step 1

⏱ ~5 minutes

Don't start drawing. Ask questions. The interviewer is testing your judgment, not your speed.

Functional requirements: What does the system do? Which features are in scope?
Non-functional requirements: Scale (DAU, QPS), latency targets, availability target (99.9%? 99.99%?)
Constraints: Read-heavy or write-heavy? Real-time or batch? Global or single-region?
Who are the users? End users, internal services, third-party developers?

💡 Interview tip

Write your requirements on the whiteboard. The interviewer will correct you if you're off-track — that's the point.

Step 2

⏱ ~5 minutes

Show the interviewer you understand scale. Round aggressively — precision doesn't matter, magnitude does.

Quick reference

See the Estimation Cheat Sheet for latency numbers and power-of-two table.

Step 3

⏱ ~20 minutes

This is the core of the interview. Draw the architecture and walk through the main flows.

API design: Define the key endpoints (2–4 max)
Data model: Key entities, relationships, choice of database
Architecture diagram: Client → LB → Services → Cache → DB (start simple, add components as needed)
Walk through flows: Trace 1–2 critical paths (e.g., "what happens when a user posts a tweet?")

💡 Interview tip

Start with the simplest design that works, then evolve it. Don't jump to microservices on slide one.

Step 4

⏱ ~15 minutes

The interviewer will point you at a component. Go deep. This is where you differentiate yourself.

Interview Framework