Before Interview

System Design Interview Cheat Sheet

Harold

Harold

— 2 min read
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System Design Interview Cheat Sheet 
This is the short version of system design interview prep.
Use it before a mock interview, before a real interview, or anytime you need to reset your structure quickly.

The basic interview flow

Most system design interviews can follow this structure:

Requirements → APIs / Data Model → High-Level Design → Deep Dives → Wrap-up

A simple time split for a 50-minute interview:

Requirement checklist

Ask a few useful questions. Do not ask too many.

Good questions:

  • What are the core features?
  • Who are the users?
  • What scale should we support?
  • What is the latency target?
  • Is strong consistency required?
  • Can some data be eventually consistent?
  • Are there features we should ignore for now?

A good phrase:

I’ll focus on the core flow first, then we can go deeper into scale and reliability.

Common building blocks

Deep dive checklist

When the simple design works, ask:

  • What breaks at scale?
  • Where is the bottleneck?
  • What data is hot?
  • What can be cached?
  • What can be async?
  • What needs strong consistency?
  • What can fail?
  • What should we monitor?

Use this format:

Problem → Option A → Option B → Tradeoff → My choice

Common tradeoffs

  • Cache improves latency, but can cause stale data.
  • Message queue improves reliability, but adds eventual consistency.
  • Sharding increases capacity, but makes queries harder.
  • Strong consistency is safer, but may reduce availability or increase latency.
  • CDN improves global performance, but makes invalidation harder.
  • Distributed locks can prevent conflicts, but add complexity.

Final takeaway

In an interview, clear structure beats random depth.

A strong candidate does not just name components. A strong candidate explains:

  • why the component is needed,
  • what problem it solves,
  • what tradeoff it introduces,
  • and how it fits into the full system.

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