Design a Distributed Rate-Limiting Service

Company: Pinterest

Role: Software Engineer

Category: System Design

Difficulty: medium

Interview Round: Online Assessment

Quick Answer: Design a distributed rate limiter for per-user, per-tenant, route, and global API policies under a tight latency budget. Make accuracy and availability trade-offs explicit across token algorithms, atomic counters, sharding, hot keys, local leases, bounded regional overshoot, partitions, and fail-open or fail-closed behavior.