Architect a scalable Feed Generation Engine
Last updated: August 7, 2025
Quick Overview
Design a scalable feed generation system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Capital One
August 7, 202531
13
4,722 solved
Design a scalable feed generation system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Capital One typically last 45-60 minutes. You are expected to drive the conversation, starting from requirements gathering through to a detailed architecture. The interviewer will evaluate your ability to handle ambiguity and make practical engineering decisions.
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
- How would you handle schema migrations with zero downtime?
- How would you optimize costs as the system scales?
- How would you implement rate limiting to protect the system?
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Requirements
Functional Requirements
- Feed Generation: The system must generate personalized feeds for users based on their transaction history, preferences, and interactions.
- Real-time Updates: U...
Capacity Estimation
Back-of-Envelope Calculations
Assuming Capital One has approximately 30 million active users:
- Requests per second (QPS): If each user fetches their feed once every minute, the total requests...
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