Build a event-driven Feature Flag Pipeline
Last updated: October 11, 2025
Quick Overview
Design a event-driven feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Zillow
October 11, 202523
14
4,073 solved
Design a event-driven feature flag system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This is a common system design question asked during Technical Screen at Zillow. The interviewer expects you to demonstrate your ability to design large-scale distributed systems, make well-reasoned trade-offs, and communicate your thought process clearly. Zillow values engineers who can think about scalability from day one.
What the Interviewer Expects
- Clearly define functional and non-functional requirements
- Propose a reasonable high-level architecture with core components
- Choose appropriate data storage solutions with basic justification
- Discuss basic scaling strategies (horizontal scaling, caching)
- Identify potential bottlenecks and suggest simple solutions
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 monitoring and alerting would you set up on day one?
- How would you optimize costs as the system scales?
- How do you ensure data consistency across multiple services?
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Requirements
Functional Requirements
- Feature Flag Management: Ability to create, update, and delete feature flags dynamically.
- Targeting Rules: Support for user segmentation based on attributes (...
Capacity Estimation
Assuming Zillow has approximately 200 million monthly active users and we expect 50% of them to interact with the feature flag system:
- Daily Requests: 200 million * 0.5 = 100 million unique inte...
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