Design Payment Infrastructure for mobile apps
Last updated: April 5, 2026
Quick Overview
Design a multi-tenant payment system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
Instacart
April 5, 2026526
6
3,487 solved
Design a multi-tenant payment system that handles millions of requests. Discuss trade-offs in consistency, availability, and performance.
This fundamentals question from Instacart's System Design Round tests whether you can reason about software design at a deep level. The interviewer expects discussion of maintainability, testability, and operational considerations.
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 document this for other engineers?
- How would you measure the performance of this component in production?
- What testing strategy would you use for this component?
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Core Design Principles
In designing a multi-tenant payment infrastructure for Instacart, the following core design principles come into play:
- Single Responsibility Principle (SRP): Each component in the system shoul...
Architecture
For Instacart's payment infrastructure, I propose a microservices architecture that includes the following components:
- API Gateway: Acts as the entry point for all payment requests, routing th...
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