How to Approach a System Design (HLD) Interview

A 7-step framework for high-level system design interviews — from requirements to deep-dive on the most challenging components.

#interview tips#system design#hld#estimation#framework

Field Note - Real-world Analogy

Think of it like this

“Like designing a city. You first agree on what the city needs (requirements). Then the scale — a town of 10,000 vs a metropolis of 10M (non-functional). You estimate land, infrastructure needs (estimation). Sketch the major zones — residential, commercial, transport (high-level architecture). Plan the road and utility network (data model). Design the subway system in detail (deep dive). Identify where traffic jams will occur and how to prevent them (bottlenecks).”

Field Observations - Key Topics Covered

Step 1 — Gather functional requirements (3 min): What does the system do? For Twitter: users can post tweets, follow others, see a timeline. List the 3-5 most important features. Explicitly say "I'll focus on these and deprioritize X" — this shows scoping ability.

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