Design a Task Scheduling for Twilio
Last updated: March 9, 2026
Quick Overview
Design a event-driven task scheduling system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Twilio
March 9, 202699
14
4,864 solved
Design a event-driven task scheduling system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Twilio asks this during the Onsite 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
- 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 ensure fairness and reduce bias in the model?
- How would you debug a model that works well offline but poorly online?
- What would you do if model performance degrades over time?
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Requirements
- Functional Requirements:
- Schedule tasks for Twilio services (e.g., SMS, voice calls) based on predefined user criteria.
- Allow users to define task parameters such as frequency, time zone...
Capacity Estimation
Assuming Twilio handles about 1 billion messages a day (SMS, calls, etc.) and that 10% of these require task scheduling:
- Daily Task Requests: 100 million requests.
- Peak Load Estimation: If...
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