Design a Distributed Rate-Limiting Service
Last updated: July 2, 2026
Quick Overview
Design a distributed rate-limiting service that can control the number of requests a user can make to an API within a specified timeframe.
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Design a distributed rate-limiting service that can control the number of requests a user can make to an API within a specified timeframe.
This question is typically asked in the online assessment round for software engineering candidates at Pinterest to evaluate their system design skills. The interviewer is looking for the candidate's ability to think through the architecture of a distributed system, understand the challenges of rate limiting, and propose a scalable solution that can handle high traffic while ensuring fair usage policies.
What the Interviewer Expects
- Identify requirements such as request limits and time windows.
- Propose a high-level architecture including components like API gateways and data stores.
- Discuss the trade-offs of different rate-limiting algorithms (e.g., token bucket, leaky bucket).
- Explain how to handle distributed state and synchronization across multiple instances.
- Address potential scaling issues and how to mitigate them.
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
- How would you handle burst traffic in your design?
- What would you do if the rate-limiting service becomes a bottleneck?
- Can you explain how you would implement a sliding window rate limit?
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Practice System Design ProblemsSample Answer
Requirements
To design a distributed rate-limiting service, we first need to establish the requirements. We need to define the maximum number of requests a user can make in a specific time frame, such as 100 reque...
High-Level Design
The architecture can be broken down into several components:
- API Gateway: This will serve as the entry point for all requests and will enforce rate limits before forwarding requests to backend ...
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