Application Programming Interface Design and Integration Questions

Designing Application Programming Interfaces and selecting communication protocols to meet functional and non functional requirements. Candidates should be able to evaluate and choose between Representational State Transfer style resource oriented interfaces, Graph Query Language approaches, remote procedure call frameworks such as Google Remote Procedure Call, and message based or event driven integration patterns. Discussion should cover protocol and format trade offs including latency, throughput, consistency and ordering, binary versus text serialization formats such as protocol buffers or JavaScript Object Notation, developer ergonomics, client diversity, and resource consumption. Core design topics include contract design and schema evolution, versioning and backward compatibility strategies, pagination, filtering, sorting and error handling conventions, authentication and authorization models, rate limiting and quota strategies, caching choices, and gateway or proxy patterns. Integration concerns include direct synchronous calls, asynchronous message based decoupling, event streaming, and web hooks, plus client and server software development kits and data transformation between layers. Candidates should also explain resilience and reliability patterns such as timeouts, retries, circuit breaker and bulkhead techniques, and describe testing, monitoring and observability approaches including logging, metrics and distributed tracing. Finally, discussion should connect API and protocol choices to coupling, scalability, operational complexity, security posture, and developer productivity.

EasyTechnical

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Explain the semantic meanings of HTTP methods GET, POST, PUT, PATCH, DELETE and when each should be used in a RESTful API. Include which methods are idempotent and safe, map common CRUD actions to methods, and list typical HTTP status codes for create (201), success (200), no-content (204), bad request (400), not found (404), and conflict (409). Discuss idempotency implications for client retries.

HardTechnical

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Design an event streaming pipeline using Kafka (or equivalent) that guarantees ordering where required and provides at-least-once or exactly-once processing semantics for critical financial events. Discuss partitioning strategy, use of producer idempotence, Kafka transactions, consumer offsets, and the practical trade-offs and pitfalls of implementing exactly-once end-to-end.

HardTechnical

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Explain how to implement circuit breakers, bulkheads, and graceful fallbacks in an API ecosystem. For each pattern describe triggers (error rate, latency), configuration (rolling windows, thresholds), fallback strategies for degraded functionality, and how to safely test and tune these patterns in staging before production rollout.

HardSystem Design

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Design a global distributed rate limiter that guarantees a client cannot exceed its quota even when requests arrive concurrently across multiple regions. Discuss trade-offs between correctness and latency, use of consensus protocols (Raft/Paxos), leader election, local fast-paths, fallback behavior when the limiter is unavailable, and how to fail open or closed safely.

HardTechnical

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Design a comprehensive testing strategy for APIs at scale: where to place unit, integration, contract, end-to-end, load, chaos, and smoke tests in the CI/CD pipeline. Explain how to keep tests fast and reliable, how to use mocks vs real dependencies, and how to structure staging environments for realistic testing without affecting production data.

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