Architect a scalable Feature Flag Engine
Last updated: October 4, 2025
Quick Overview
Design a scalable feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
HRT
October 4, 20257
9
2,586 solved
Design a scalable feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Software engineering fundamentals questions at HRT 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
- How would this design change if the team size doubled?
- What testing strategy would you use for this component?
- How would you handle backward compatibility?
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Core Principles
Start by identifying which engineering principles are most relevant: **SOLID Principles**: Single Responsibility (one reason to change), Open/Closed ...
Design Approach
**API Design**: Define clear interfaces before implementation. Use RESTful conventions for HTTP APIs. Version your APIs from the start. Return meaning...
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