Architect a low-latency Rate Limiting Engine
Last updated: February 22, 2026
Quick Overview
Design a low-latency rate limiting system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
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Design a low-latency rate limiting system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Pinterest 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
- Clearly define functional and non-functional requirements
- Propose a reasonable high-level architecture with core components
- Choose appropriate data storage solutions with basic justification
- Discuss basic scaling strategies (horizontal scaling, caching)
- Identify potential bottlenecks and suggest simple solutions
Key Topics to Cover
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 happens if one of your database nodes goes down?
- How would you handle schema migrations with zero downtime?
- What would the deployment pipeline look like for this system?
- How would you handle a region-wide outage?
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Requirements
Functional Requirements
- Rate Limiting: The system must limit the number of requests a user can make to a specific endpoint within a given time frame (e.g., 100 requests per minute).
- **Us...
Capacity Estimation
Assuming Pinterest has 100 million active users and each user makes an average of 10 requests per minute, we can estimate the total requests:
- Total Requests per Minute: 100 million users * 10 r...
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