Architect a geo-distributed Feature Flag Engine
Last updated: October 23, 2025
Quick Overview
Design a geo-distributed feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
PlanetScale
October 23, 20250
5
1,720 solved
Design a geo-distributed feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
PlanetScale asks this during the Technical Screen to assess your depth in software engineering. They want to see understanding of design patterns, system architecture, and the trade-offs involved in different technical approaches.
What the Interviewer Expects
- Explain the concept clearly with a practical example
- Discuss when and why to apply this principle
- Identify common mistakes and anti-patterns
- Compare with alternative approaches
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 you document this for other engineers?
- How would you handle backward compatibility?
- How would this design change if the team size doubled?
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Core Design Principles
For a geo-distributed feature flag engine, the primary design principles are Separation of Concerns and Single Responsibility Principle (SRP). Separation of Concerns allows us to distinctly ma...
Architecture
The architecture for the geo-distributed feature flag engine will follow a Microservices approach, leveraging services like a Feature Flag Service, a User Context Service, and a **Geo-Repl...
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