Design a scalable Messaging System
Last updated: May 5, 2026
Quick Overview
Design a scalable messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Instacart
May 5, 20260
7
625 solved
Design a scalable messaging system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Instacart 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
- 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?
- What testing strategy would you use for this component?
- How would you document this for other engineers?
- How would you handle backward compatibility?
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Core Design Principles
For a scalable messaging system at Instacart, the key design principles include:
- Separation of Concerns: This principle ensures that different components of the messaging system (e.g., message ...
Architecture
The proposed architecture for Instacart's messaging system consists of:
- Producers: Services that send messages (e.g., order updates, inventory changes).
- Message Broker: A distributed messa...
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