System designMediumsd-p019

Subject ConsistencyLevel Mid–Senior~45 minCommon in Databases & SQL interviewsIndustries Technology, Software development

Question

Design a feature-flag and dynamic-configuration service that serves flag evaluations to thousands of app servers with single-digit-millisecond reads and supports gradual rollouts and targeting.

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.