Design a global high-throughput rate limiter
Overview
This question evaluates distributed systems design, scalability, consistency trade-offs, rate-limiting algorithms, data modeling, and operational competencies required to build a global, low-latency multi-region service.
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Sep 6, 2025, 12:00 AM
Software Engineer
Onsite
System Design
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System Design: Global, High-Throughput Rate Limiter
Context
You are designing a global, multi-region rate-limiting service that enforces quotas:
- Per-user (across all APIs)
- Per-API (across all users)
- Per-user-per-API (composite)
The system must be low-latency, tolerate bursts, and operate across multiple regions.
Requirements
Design and justify:
- Algorithm choice (e.g., token bucket vs. leaky bucket) with burst tolerance and latency considerations.
- Data model for quotas, runtime state, and metrics.
- Partitioning and sharding strategy for a global deployment.
- Clock/time-window semantics (fixed vs. sliding windows, monotonic time handling).
- Consistency trade-offs (global correctness vs. latency) and how you bound overages.
- Hot-key handling strategies.
- Scaling strategies and capacity planning math, including how many machines are required if traffic doubles (2×), with clear assumptions and formulas.
- Failure modes and mitigations.
- Backpressure behavior and client guidance.
- Observability: metrics, tracing, dashboards, and alerts.
- APIs for configuration and metrics.
Assume a mixed workload with both regional and global traffic patterns, and that some users may send traffic from multiple regions concurrently.
Solution
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