Design a real-time Notification System
Last updated: December 19, 2025
Quick Overview
Design a real-time notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Apple
December 19, 2025175
8
1,869 solved
Design a real-time notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Software engineering fundamentals questions at Apple test your understanding of core CS concepts and their practical application. This System Design Round question evaluates how you apply engineering principles to build maintainable, scalable software.
What the Interviewer Expects
- Apply engineering principles to a realistic design scenario
- Discuss trade-offs between different approaches with concrete examples
- Demonstrate understanding of testability, maintainability, and extensibility
- Connect theoretical concepts to production engineering practices
- Discuss how the approach scales with team and codebase size
Key Topics to Cover
How to Approach This
- Apply SOLID principles. Single Responsibility makes code testable, Open/Closed makes it extensible.
- Choose data structures based on access patterns, not familiarity.
- Prefer immutable data and message passing over shared mutable state for concurrency.
- Design APIs with RESTful conventions, versioning, meaningful errors, and pagination from day one.
Possible Follow-up Questions
- What testing strategy would you use for this component?
- How would you measure the performance of this component in production?
- How would you handle backward compatibility?
- How would you document this for other engineers?
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Core Design Principles
For the real-time notification system, the core design principles applicable are:
- SOLID Principles: Specifically, the Single Responsibility Principle (SRP) ensures that each component of the n...
Architecture
The architectural approach for the notification system will be a Microservices Architecture:
- Components:
- API Gateway: Entry point for all requests, handling load balancing and rou...
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