Design a Feature Flag for Visa
Last updated: February 10, 2026
Quick Overview
Design a distributed feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Visa
February 10, 2026260
12
1,685 solved
Design a distributed feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Software engineering fundamentals questions at Visa test your understanding of core CS concepts and their practical application. This Onsite 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 you handle backward compatibility?
- How would this design change if the team size doubled?
- How would you measure the performance of this component in production?
- What testing strategy would you use for this component?
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Core Design Principles
For the distributed feature flag system at Visa, we will apply the SOLID principles:
- Single Responsibility Principle: Each component (e.g., flag management, feature evaluation, and logging...
Architecture
The architecture for the feature flag system at Visa will follow a microservices approach. The primary components will include:
- Feature Management Service: Responsible for creating, updati...
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