Design Notification Infrastructure for mobile apps
Last updated: July 15, 2025
Quick Overview
Design a geo-distributed notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Vercel
System Design
Software Engineer
Vercel
July 15, 2025Software Engineer
Onsite
System Design
Medium
226
8
3,916 solved
Design a geo-distributed notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This ML system design question from Vercel's Onsite tests your ability to think about ML systems at scale. The interviewer expects discussion of data quality, feature stores, model serving infrastructure, and A/B testing strategy.
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
Online vs offline evaluation
Feedback loops and model retraining
Model serving and latency optimization
Model selection and architecture
ML objective formulation and metric selection
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 a 10x increase in prediction requests?
- How would you run A/B tests on different model versions?
- How would you ensure fairness and reduce bias in the model?
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Requirements
- Functional Requirements:
- Send push notifications to mobile devices based on user behavior and preferences.
- Support geo-targeted notifications for location-based services.
- Al...
Capacity Estimation
- User Base: Assume 10 million active users.
- Notifications per User: Average of 5 notifications per day.
- Total Notifications: 10M users * 5 notifications = 50 million notifications...
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