Architect a high-throughput Notification Engine
Last updated: February 10, 2026
Quick Overview
Design a high-throughput notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Zillow
February 10, 202619
7
376 solved
Design a high-throughput notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
ML system design at Zillow goes beyond model selection. This Onsite question evaluates your ability to design end-to-end ML pipelines, from data collection to model serving, while considering production constraints like latency and reliability.
What the Interviewer Expects
- Design the full ML lifecycle from data collection to model monitoring
- Address cold start, exploration/exploitation, and model freshness
- Discuss multi-objective optimization and ranking systems
- Plan for model debugging, fairness, and bias mitigation
- Design the feature store and training pipeline for scale
- Address model versioning, canary deployments, and rollback strategies
- Discuss the data flywheel and long-term system evolution
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 debug a model that works well offline but poorly online?
- How would you run A/B tests on different model versions?
- What is your model retraining strategy?
Practice a Similar Problem on Codemia
Solve a related problem with our interactive workspace, get AI feedback, and view detailed solutions.
Solve on CodemiaSample Answer
Requirements
Functional Requirements:
- User Notifications: Send personalized notifications to users regarding new property listings, price changes, and rental opportunities.
- Real-time Processing: ...
Capacity Estimation
Assuming Zillow has approximately 200 million active users and each user receives an average of 10 notifications per day:
- Total Notifications per Day: 200M users * 10 notifications = 2 billion n...
Submit Your Answer
