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 Clarification
Before diving into the architecture, clarify the scope with the interviewer. For Feature Flag Infrastructure for mobile apps, key functional requireme...
Capacity Estimation
Estimate the scale to drive design decisions. Assume 100M DAU with an average of 10 actions per user per day = 1B requests/day ~ 12K QPS average, ~36K...
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