Design a Notification Service
Last updated: December 31, 2025
Quick Overview
Design a low-latency notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Twilio
System Design
Software Engineer
Twilio
December 31, 2025Software Engineer
System Design Round
System Design
Medium
234
4
1,057 solved
Design a low-latency notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at Twilio typically last 45-60 minutes. You are expected to drive the conversation, starting from requirements gathering through to a detailed architecture. The interviewer will evaluate your ability to handle ambiguity and make practical engineering decisions.
What the Interviewer Expects
- Systematically gather requirements and estimate capacity (QPS, storage, bandwidth)
- Design a scalable architecture with clear component responsibilities
- Make well-reasoned database and caching decisions with trade-off analysis
- Address consistency vs availability trade-offs specific to the use case
- Discuss partitioning strategy, replication, and data modeling
- Cover failure handling, monitoring, and alerting strategies
Key Topics to Cover
Failure handling and fault tolerance
Partitioning and sharding strategies
High-level architecture and component design
Monitoring, logging, and alerting
API design and rate limiting
Caching strategies (local, distributed, CDN)
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 region-wide outage?
- How would you implement rate limiting to protect the system?
- What would the deployment pipeline look like for this system?
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Requirements
Functional Requirements
- Send Notification: The system should allow users to send notifications via SMS, Email, or Push notifications.
- Receive Notifications: Users should be able to r...
Capacity Estimation
Back-of-Envelope Calculations
- Daily Notifications: 10 million notifications/day.
- Peak Load: 500 notifications/second.
- Storage: Assuming average notification size is 1 KB:
- Dai...
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