Design a Global Distributed Rate Limiter

Interview Question

Design a globally distributed rate limiter for multi-region APIs supporting per-user, per-IP, and per-endpoint quotas.

Key Points to Cover

Evaluation Rubric

Chooses and applies rate-limit algorithms25% weight

Designs scalable/consistent state storage25% weight

Handles failures and multi-region issues25% weight

Monitoring, audit, and safety levers25% weight

Hints

Common Pitfalls to Avoid

⚠️Attempting to achieve strong global consistency for every rate limit check, which introduces unacceptable latency and complexity.
⚠️Ignoring the critical need for hot key mitigation, leading to single points of contention and performance bottlenecks in the distributed state store.
⚠️Failing to design a dedicated control plane for policy management, making rate limit rule updates and deployments cumbersome and error-prone.
⚠️Not adequately addressing cross-region latency for synchronous operations, which can severely degrade API performance for users far from the primary region.
⚠️Overlooking graceful degradation strategies, leading to either complete system failure (fail-closed) or uncontrolled abuse (fail-open without limits) during rate limiter service outages.

Potential Follow-up Questions