Architect a event-driven Rate Limiting Engine
Last updated: April 6, 2026
Quick Overview
Design a event-driven rate limiting system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Expedia
April 6, 202610
7
2,400 solved
Design a event-driven rate limiting system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Expedia asks this during the System Design Round to assess your understanding of the full ML lifecycle. They want to see how you translate a business problem into an ML objective, design the feature pipeline, and plan for model monitoring and retraining.
What the Interviewer Expects
- Map the business problem to a concrete ML objective
- Propose reasonable features and a baseline model
- Discuss basic model evaluation metrics
- Outline a simple serving architecture
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 would you do if model performance degrades over time?
- How would you run A/B tests on different model versions?
- How would you debug a model that works well offline but poorly online?
- How would you handle the cold start problem?
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Requirements
Functional Requirements:
- Request Tracking: Ability to track and log incoming requests for various APIs.
- Rate Limiting: Implement rate limiting based on user identity, IP address, and...
Capacity Estimation
Assuming Expedia handles 10 million requests per day, we can break this down:
- Peak Traffic: Assume peak hours constitute 20% of daily traffic, leading to:
- 10 million requests/day / 24 ho...
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