Design a large-scale A/B Testing Platform
Last updated: January 29, 2026
Quick Overview
Design a scalable a/b testing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Microsoft
January 29, 20260
5
3,070 solved
Design a scalable a/b testing system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Microsoft asks this during the Technical Screen to assess your understanding of the full ML lifecycle. They want to see how you translate a business problem into an ML objective, design the feature pipeline, and plan for model monitoring and retraining.
What the Interviewer Expects
- Define clear ML objectives with appropriate loss functions and metrics
- Design a comprehensive feature engineering pipeline
- Discuss model selection with trade-offs (complexity vs interpretability vs latency)
- Plan online and offline evaluation strategies including A/B testing
- Address serving infrastructure: batch vs real-time, latency requirements
- Consider data quality, labeling strategy, and feedback loops
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 run A/B tests on different model versions?
- How would you ensure fairness and reduce bias in the model?
- What is your model retraining strategy?
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Requirements
Functional Requirements
- User Segmentation: Ability to segment users based on demographics, behavior, and previous interactions.
- Experiment Creation: UI for product teams to create, m...
Capacity Estimation
Assuming 1 million active users with an average of 10 interactions per user per day, we have:
- Total Interactions per Day: 1,000,000 users * 10 interactions/user = 10,000,000 interactions/day.
- ...
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