Design a low-latency Notification System
Last updated: January 23, 2026
Quick Overview
Design a low-latency notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
HRT
System Design
Software Engineer
HRT
January 23, 2026Software Engineer
System Design Round
System Design
Hard
95
13
3,078 solved
Design a low-latency notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
HRT asks this during the System Design Round to assess your architectural thinking. They want to see how you decompose a complex problem, choose appropriate technologies, and reason about failure modes. Strong candidates proactively discuss monitoring, alerting, and operational concerns.
What the Interviewer Expects
- Drive the design discussion proactively with minimal interviewer guidance
- Perform detailed capacity estimation and use it to inform design decisions
- Design for global scale with multi-region deployment and data consistency
- Deep dive into 2-3 critical components with implementation-level detail
- Address complex trade-offs: CAP theorem, eventual consistency, conflict resolution
- Discuss operational excellence: deployment strategy, chaos engineering, SLOs/SLIs
- Propose a phased rollout plan from MVP to full-scale system
Key Topics to Cover
High-level architecture and component design
Requirements gathering and capacity estimation
Security and authentication
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 implement rate limiting to protect the system?
- How do you ensure data consistency across multiple services?
- How would you handle a region-wide outage?
- What monitoring and alerting would you set up on day one?
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Requirements
- Functional Requirements:
- Support sending notifications to users in real-time (within milliseconds).
- Handle various notification types: alerts, messages, and system updates.
- Enable us...
Capacity Estimation
- User Base: Assume 50 million users globally.
- Notification Frequency: Average 2 notifications per user per day, with peaks during events (up to 10 notifications).
- **Peak Load Calculati...
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