TL;DR — Feature Flags Service

Design a feature flags service that allows engineering teams to control feature visibility in production without code deployments. Product managers and engineers define flags with targeting rules (e.g., enable for 10% of users, enable for beta testers, enable for users in EU), and client SDKs evaluate these rules locally with near-zero latency. The system powers both simple kill switches and complex gradual rollouts with A/B testing. Key features: Create, update, and archive feature flags with boolean or multivariate variations. Targeting rules: user attributes, segments, percentage rollout, schedule-based activation.