Design Rate Limiting Infrastructure for mobile apps
Last updated: January 21, 2026
Quick Overview
Design a fault-tolerant rate limiting system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
SentinelOne
January 21, 2026494
11
2,522 solved
Design a fault-tolerant rate limiting system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at SentinelOne 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
- 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
- What happens if one of your database nodes goes down?
- What monitoring and alerting would you set up on day one?
- How would you handle a 10x increase in traffic overnight?
- How would you migrate from a monolithic to a microservices architecture?
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Requirements
Functional Requirements
- Rate Limiting: The system must enforce rate limits per user based on user tiers (e.g., free, premium).
- Dynamic Configurations: Admins should be able to update...
Capacity Estimation
Assuming SentinelOne serves 10 million active users, with an average of 5 requests per user per minute:
- Total Requests per Minute: 10,000,000 users * 5 requests/user = 50,000,000 requests/minute...
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