The System Design Interview Framework
1 min read
A Repeatable Framework
The biggest mistake candidates make is jumping straight to boxes and arrows. Use a structured method so you never freeze.
1. Requirements (5 min)
Clarify scope out loud:
- Functional: the 2–3 core features (ignore the rest).
- Non-functional: scale, latency, availability, consistency needs.
- Constraints: read-heavy or write-heavy? Global or regional?
Ask questions. Interviewers want you to narrow the problem.
2. Estimation (5 min)
Back-of-the-envelope math: DAU → QPS → storage → bandwidth. This drives every later decision.
3. High-level design (10 min)
Draw the major components and a request's path: client → load balancer → service → cache → database. Keep it simple first.
4. Deep dive (15 min)
The interviewer picks a component. Be ready to detail the data model, how you shard, your caching strategy and failure handling.
5. Wrap up (5 min)
Name the bottlenecks, the trade-offs you made, and what you'd improve with more time.
A reusable checklist
- Read/write ratio identified
- Single points of failure removed
- Data partitioning strategy chosen
- Caching layer justified
- Consistency model stated explicitly
- Monitoring / metrics mentioned
Memorise the flow, not a specific answer. The flow is what keeps you calm.