Architect a fault-tolerant Chat Engine
Last updated: February 22, 2026
Quick Overview
Design a fault-tolerant chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Zscaler
February 22, 202651
5
2,591 solved
Design a fault-tolerant chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Software engineering fundamentals questions at Zscaler 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
- How would you measure the performance of this component in production?
- How would you handle backward compatibility?
- How would this design change if the team size doubled?
- How would you document this for other engineers?
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Core Design Principles
In designing a fault-tolerant chat engine for Zscaler, the following core design principles apply:
- Separation of Concerns: This principle ensures that different aspects of the chat system (e.g....
Architecture
The architecture for the chat engine will leverage a microservices approach:
- Frontend: A React-based web app that communicates with the backend via RESTful APIs, providing a responsive user expe...
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