Design Rate Limiting Infrastructure for microservices
Last updated: January 21, 2026
Quick Overview
Design a distributed rate limiting system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Cruise
System Design
Software Engineer
Cruise
January 21, 2026Software Engineer
Technical Screen
System Design
Hard
190
13
2,572 solved
Design a distributed rate limiting system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Cruise typically last 45-60 minutes. You are expected to drive the conversation, starting from requirements gathering through to a detailed architecture. The interviewer will evaluate your ability to handle ambiguity and make practical engineering decisions.
What the Interviewer Expects
- Drive the design discussion proactively with minimal interviewer guidance
- Perform detailed capacity estimation and use it to inform design decisions
- Design for global scale with multi-region deployment and data consistency
- Deep dive into 2-3 critical components with implementation-level detail
- Address complex trade-offs: CAP theorem, eventual consistency, conflict resolution
- Discuss operational excellence: deployment strategy, chaos engineering, SLOs/SLIs
- Propose a phased rollout plan from MVP to full-scale system
Key Topics to Cover
Database selection and data modeling
Security and authentication
Load balancing and horizontal scaling
High-level architecture and component design
API design and rate limiting
Consistency models and replication
How to Approach This
- Start by clarifying functional and non-functional requirements with the interviewer.
- Estimate the scale: QPS, storage, bandwidth. This drives your design decisions.
- Draw a high-level architecture first, then deep dive into 1-2 critical components.
- Discuss trade-offs explicitly (e.g., consistency vs availability, SQL vs NoSQL).
- Address failure scenarios, monitoring, and how the system handles 10x traffic spikes.
Possible Follow-up Questions
- What monitoring and alerting would you set up on day one?
- How would you optimize costs as the system scales?
- How would you handle a 10x increase in traffic overnight?
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Requirements
- Functional Requirements:
- The system must limit requests to defined thresholds for different user roles (e.g., free users vs. premium users).
- Provide APIs for microservices to check the r...
Capacity Estimation
- Assume Cruise has 10 million users, with an average of 10 requests per user per minute.
- Total requests per minute = 10 million * 10 = 100 million.
- With a peak load of 10x, we estimate 1 billion ...
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