Design a Chat Service
Last updated: January 30, 2026
Quick Overview
Design a fault-tolerant chat system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
ServiceNow
January 30, 2026133
5
2,601 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 ServiceNow 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 this design change if the team size doubled?
- How would you document this for other engineers?
- What are the security implications of this design?
- How would you handle backward compatibility?
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Core Design Principles
In designing the chat service for ServiceNow, we should adhere to the following core design principles:
- Single Responsibility Principle (SRP): Each component of the chat system should have a s...
Architecture
For the chat service at ServiceNow, we can adopt a microservices architecture consisting of the following components:
- API Gateway: Acts as the entry point for all client requests, routing them...
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