Architect a scalable Messaging Engine
Last updated: February 18, 2026
Quick Overview
Design a scalable messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
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Design a scalable messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Reddit asks this during the Onsite 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 this design change if the team size doubled?
- How would you handle backward compatibility?
- How would you document this for other engineers?
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Core Principles
Start by identifying which engineering principles are most relevant: **SOLID Principles**: Single Responsibility (one reason to change), Open/Closed ...
Design Approach
**API Design**: Define clear interfaces before implementation. Use RESTful conventions for HTTP APIs. Version your APIs from the start. Return meaning...
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