Design a Notification Service
Last updated: April 18, 2026
Quick Overview
Design a scalable notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
DoorDash
April 18, 202638
14
4,196 solved
Design a scalable notification system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
DoorDash asks this during the System Design Round to assess your depth in software engineering. They want to see understanding of design patterns, system architecture, and the trade-offs involved in different technical approaches.
What the Interviewer Expects
- Explain the concept clearly with a practical example
- Discuss when and why to apply this principle
- Identify common mistakes and anti-patterns
- Compare with alternative approaches
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
- How would you document this for other engineers?
- How would you measure the performance of this component in production?
- What are the security implications of this design?
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Core Design Principles
For the design of the Notification Service at DoorDash, we will focus on the following core design principles:
- SOLID Principles: Specifically, the Single Responsibility Principle (SRP) and Ope...
Architecture
The architecture of the Notification Service will be based on microservices, which allows for scalability and independent deployment:
- Service Components: We will have a central Notification Ma...
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