System designMediumsd-g577

Subject System designLevel Mid–Senior~35 minCommon in Distributed systems interviewsIndustries Software development, Technology

Question

Design a link-unfurling / URL-preview service for a chat app (Slack-like) that, when a user pastes a URL, fetches the page and shows a rich preview (title, description, image). Scale: ~30K URLs/sec at peak, many duplicate URLs (news links shared widely), target preview render <300ms when cached. Requirements: don't fetch the same URL repeatedly, handle slow/huge/malicious target sites without hanging or being abused as a proxy, and degrade gracefully when a site has no metadata.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.