Design a large-scale A/B Testing Platform
Last updated: July 22, 2025
Quick Overview
Design a distributed a/b testing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Compass
July 22, 2025132
3
4,826 solved
Design a distributed a/b testing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Compass asks this during the Onsite 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
- 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 happens if one of your database nodes goes down?
- How would you handle schema migrations with zero downtime?
- What monitoring and alerting would you set up on day one?
- How would you optimize costs as the system scales?
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Requirements
Functional Requirements
- Experiment Creation and Management: Users must be able to create, manage, and analyze A/B tests through a user-friendly interface.
- Traffic Allocation: Ability...
Capacity Estimation
Assuming Compass has an average of 10 million users, and each user visits the platform 5 times a day, we can estimate:
- Total Requests per Day: 10 million users * 5 visits = 50 million requests/d...
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