Design and evolve application programming interfaces so they meet functional requirements while minimizing disruption to clients and services. Core skills include designing resource oriented endpoints, choosing and implementing versioning strategies, and preserving backward compatibility. Candidates should understand versioning approaches such as embedding a version in the endpoint path, using request headers to select versions, and designing non breaking changes so explicit version bumps are avoided. Important topics include idempotency, pagination, filtering, sorting, error response design, status semantics, rate limiting, authentication and authorization, and considerations for low bandwidth or mobile clients. At senior levels discuss operational and lifecycle concerns: deprecation policies and timelines, migration plans, compatibility testing, handling multiple client versions simultaneously in production, rolling deployments and coexistence strategies, contract testing, and alternatives such as remote procedure call frameworks. Expect trade off discussions around developer experience, client upgrade friction, monitoring and instrumentation for versioned traffic, and communication strategies with downstream consumers.
HardSystem Design
0 practiced
Design an audit logging and access-trail architecture for APIs in regulated industries. Requirements: record who accessed which resources, when, and what was returned (or a masked summary); logs must be tamper-evident, encrypted at rest, searchable for investigations, and comply with retention policies. Describe log schema, storage choices, indexing strategy, and integration with SIEM tools.
EasyTechnical
0 practiced
Design two pagination strategies for a 'List transactions' endpoint: offset-based and cursor-based. For each strategy provide: query parameters, sample request and JSON response (include 'items' and next page indicators), and discuss trade-offs regarding consistency, performance, and developer ergonomics. Provide a concise OpenAPI-style snippet for the cursor-based response including a 'nextCursor'.
MediumSystem Design
0 practiced
Design an observability model for versioned APIs. Which metrics, logs, and traces would you collect per API version to detect regressions introduced by new versions? Provide example SLIs (latency p95, error-rate, success-rate), labeling/tagging strategies, and alerting approaches to identify version-specific regressions quickly.
HardTechnical
0 practiced
Design a rolling deployment strategy that serves both old and new API implementations concurrently to enable gradual client migration. Requirements: percentage-based traffic routing (canary), sticky sessions when necessary, per-version observability, rollback path on error thresholds, and coordination with data schema changes. Describe how you'd implement this using Kubernetes, Istio/Envoy, and an API gateway.
MediumSystem Design
0 practiced
Design a distributed rate limiter for an API gateway that enforces both per-user limits (100 requests/min) and global limits (10,000 requests/min). Requirements: low latency, burst handling, consistency across multiple gateway instances, and per-version metrics. Describe algorithm choices, datastore options, consistency trade-offs, and failure modes.
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