Design a Notification Service
Last updated: October 23, 2025
Quick Overview
Design a distributed notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
ServiceNow
System Design
Software Engineer
ServiceNow
October 23, 2025Software Engineer
Onsite
System Design
Medium
9
13
4,386 solved
Design a distributed notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
System design interviews at ServiceNow 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
Partitioning and sharding strategies
Failure handling and fault tolerance
Monitoring, logging, and alerting
Message queues and async processing
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
- What happens if one of your database nodes goes down?
- How would you optimize costs as the system scales?
- What would the deployment pipeline look like for this system?
- How do you ensure data consistency across multiple services?
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Requirements
Functional Requirements
- User Notifications: The system should send notifications to users via email, SMS, and in-app messages.
- Batch Processing: Ability to send bulk notifications fo...
Capacity Estimation
Back-of-Envelope Calculations
- User Base: Assume 10 million active users.
- Notifications per User: Average of 3 notifications per user per day.
- Total Notifications: 10M users * ...
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