System designMediumsd-g566

Subject System designLevel Mid–Senior~40 minCommon in Databases & SQL interviewsIndustries Software development, Technology

Question

Design a multi-tenant feature-flag service used by ~5,000 customer organizations, each running their own apps. Flag evaluations happen in-app at ~500K evals/sec aggregate and must add <1ms latency (no network call on the hot path). Flags support boolean, multivariate, and percentage rollouts keyed on user attributes. Admins toggle flags in a dashboard and expect changes to propagate to running services within a few seconds. Read-heavy: ~1M reads per config write.

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

Loading whiteboard…

Run or narrate your approach, then ask the coach.