System designMediumsd-g542

Subject Feature flagsLevel Entry–Mid~30 minCommon in Distributed systems interviewsIndustries Software development, Technology

Question

Design a simple feature-flag service for one company's apps. An admin can turn a flag on or off, or enable it for a percentage of users or a specific list of users. The apps check flags on nearly every request, so the check must be fast and must not fail if the flag service is briefly unavailable. Cover the data model, how an app evaluates a flag for a given user, and how you make checks fast and resilient.

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.