Design a Chat for Doordash
Last updated: October 17, 2025
Quick Overview
Design a real-time chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Doordash
October 17, 202537
5
4,865 solved
Design a real-time chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Doordash asks this during the Technical Screen 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
- Design a complex system component applying multiple engineering principles
- Reason about system-level trade-offs: performance, reliability, developer experience
- Discuss advanced patterns: event sourcing, CQRS, distributed transactions
- Address cross-cutting concerns: observability, security, backward compatibility
- Demonstrate depth in both theoretical foundations and practical implementation
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 measure the performance of this component in production?
- What testing strategy would you use for this component?
- What are the security implications of this design?
- How would this design change if the team size doubled?
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Core Design Principles
For the real-time chat system at DoorDash, the following core design principles apply:
- Separation of Concerns: This principle helps in isolating the chat logic from other system components, ma...
Architecture
The architectural approach for the chat system at DoorDash would utilize a microservices architecture leveraging the following components:
- Frontend: A React-based web and mobile chat interface...
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