This is one of those questions that feels approachable until you realize how many directions it can go.
Start by clarifying requirements and scale, then design a system that separates flag configuration from evaluation, ensuring low-latency reads and high availability. Focus on the core components: flag management, evaluation engine, and data pipeline for metrics, while discussing trade-offs and Stripe-specific considerations like security and compliance.
Pro tip: Emphasize the importance of a kill switch and gradual rollouts to mitigate risk, and discuss how you would handle flag consistency across services to avoid inconsistent user experiences.
Ask questions to understand the expected scale (number of flags, evaluations per second), latency requirements, consistency needs, and use cases (A/B testing, kill switches, etc.).
Outline the main components: a flag management service (CRUD for flags), a rules engine for targeting, a low-latency evaluation service, and a data pipeline for analytics. Consider using a CDN or edge caching for global low-latency reads.
Design how flags are stored (e.g., key-value with rules), how targeting rules are evaluated (e.g., user attributes, percentage rollouts), and how to ensure deterministic evaluation (e.g., hashing user IDs).
Discuss how to scale the evaluation service (stateless, horizontally scalable), ensure high availability (multi-region, fallbacks), and handle flag updates without downtime (e.g., pub/sub for cache invalidation).
Discuss trade-offs between consistency and latency, push vs. pull models, and how to integrate with Stripe's infrastructure (e.g., security, audit logs, compliance).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.