Design Feature Flag Infrastructure for mobile apps
Last updated: August 9, 2025
Quick Overview
Design a distributed feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Cloudflare
August 9, 202519
12
1,058 solved
Design a distributed feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Cloudflare asks this during the Technical Screen to assess your architectural thinking. They want to see how you decompose a complex problem, choose appropriate technologies, and reason about failure modes. Strong candidates proactively discuss monitoring, alerting, and operational concerns.
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?
- How would you handle schema migrations with zero downtime?
- How would you implement rate limiting to protect the system?
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Requirements
- Functional Requirements:
- Ability to create, update, and delete feature flags through a secure admin dashboard.
- Support for targeting specific user segments based on attributes (e.g...
Capacity Estimation
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User Base:
Assume 100 million active users, with an average of 5 feature flag requests per user per session. -
Requests Per Second (QPS):
- Peak usage estimate: 10% of users ac...
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