Design a Distributed Rate Limiter

Problem Design a distributed rate limiter using a sliding-window approach that scales to millions of requests/sec with fairness across clients.

Functional requirements

• Per-client request limits.
• Sliding-window accuracy.
• Fairness across many clients.
• Low added latency on the request path.

Non-functional requirements

• Millions of req/sec across many nodes.
• Tolerate node failures and clock skew.
• Absorb bursts gracefully.

Areas to go deep

• Sliding-window log vs counter trade-offs.
• Distributed state (Redis / consistent hashing) and where the counter lives.
• Fairness, burst absorption, network latency, and clock-skew handling.
• Failure modes and graceful degradation.