Architect a high-throughput Rate Limiting Engine
Last updated: October 13, 2025
Quick Overview
Design a high-throughput rate limiting system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Square/Block
October 13, 202527
5
444 solved
Design a high-throughput rate limiting system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Software engineering fundamentals questions at Square/Block test your understanding of core CS concepts and their practical application. This System Design Round question evaluates how you apply engineering principles to build maintainable, scalable software.
What the Interviewer Expects
- Design a complex system component applying multiple engineering principles
- Reason about system-level trade-offs: performance, reliability, developer experience
- Discuss advanced patterns: event sourcing, CQRS, distributed transactions
- Address cross-cutting concerns: observability, security, backward compatibility
- Demonstrate depth in both theoretical foundations and practical implementation
Key Topics to Cover
How to Approach This
- Apply SOLID principles. Single Responsibility makes code testable, Open/Closed makes it extensible.
- Choose data structures based on access patterns, not familiarity.
- Prefer immutable data and message passing over shared mutable state for concurrency.
- Design APIs with RESTful conventions, versioning, meaningful errors, and pagination from day one.
Possible Follow-up Questions
- What testing strategy would you use for this component?
- How would you document this for other engineers?
- What are the security implications of this design?
- How would you measure the performance of this component in production?
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Core Design Principles
For a high-throughput rate limiting engine, we apply the following core design principles:
- Single Responsibility Principle (SRP): Each component of the rate limiting engine should have one res...
Architecture
The architecture of the rate limiting engine at Square/Block will consist of:
- API Gateway: Acts as the entry point for all requests, where initial rate limiting checks occur before reaching ba...
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