Design Rate Limiting Infrastructure for mobile apps
Last updated: January 21, 2026
Quick Overview
Design a scalable rate limiting system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Zillow
January 21, 202648
8
4,541 solved
Design a scalable rate limiting system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Zillow asks this during the Technical Screen to assess your architectural thinking. They want to see how you decompose a complex problem, choose appropriate technologies, and reason about failure modes. Strong candidates proactively discuss monitoring, alerting, and operational concerns.
What the Interviewer Expects
- Systematically gather requirements and estimate capacity (QPS, storage, bandwidth)
- Design a scalable architecture with clear component responsibilities
- Make well-reasoned database and caching decisions with trade-off analysis
- Address consistency vs availability trade-offs specific to the use case
- Discuss partitioning strategy, replication, and data modeling
- Cover failure handling, monitoring, and alerting strategies
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 a region-wide outage?
- How would you handle schema migrations with zero downtime?
- 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
- Rate Limiting: The system must enforce rate limits on API calls from mobile apps to prevent abuse. Limits can be defined per user or per IP address.
- **Dynamic Con...
Capacity Estimation
Estimation
Assuming Zillow has:
- 5 million active users on mobile apps.
- Each user makes an average of 10 API calls per minute during peak hours.
Calculating QPS:
- Total API calls = 5,...
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