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title: API Case Studies
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# API Case Studies

## Fundamentals and API Design
1. Designing a clean JSON CRUD API for a task manager
2. Evolving response contracts without breaking old clients
3. Standardizing API errors across microservices
4. Building predictable pagination, filtering, and sorting at scale
5. Designing idempotent create APIs for safe retries

## Security, Identity, and Abuse Prevention
1. Migrating from API keys to OAuth 2.0 with zero downtime
2. Solving authorization drift in role and permission based APIs
3. Defending public APIs with layered rate limiting and quotas
4. Securing multi-tenant APIs with strict data isolation
5. Hardening webhook endpoints with signature verification and replay protection

## Performance and Reliability
1. Reducing p99 latency using caching and cache invalidation strategies
2. Handling traffic spikes with backpressure and graceful degradation
3. Preventing duplicate side effects with idempotency keys
4. Applying timeouts, retries, and circuit breakers in distributed APIs
5. Designing resilient partial-failure handling in aggregator APIs

## Files, Media, and Large Payloads
1. Uploading images safely with pre-signed URLs and malware scanning
2. Reliable large file uploads with multipart and resumable protocols
3. Serving private media via signed URLs and short-lived access
4. Image processing pipelines: upload, transform, and CDN delivery
5. Streaming downloads for large exports without memory blowups

## Async and Event-Driven APIs
1. Converting long-running synchronous APIs into async job-based workflows
2. Designing webhook delivery with retries, dead-letter queues, and observability
3. Guaranteeing ordering and deduplication in event-driven integrations
4. Coordinating API calls and message queues with eventual consistency
5. Building status polling and callback patterns for background tasks

## Integrations and External Dependencies
1. Surviving third-party API outages with fallbacks and cached reads
2. Normalizing inconsistent partner API schemas into one internal contract
3. Building a robust API gateway for auth, routing, and policy enforcement
4. Managing API version migrations across internal and external consumers
5. Preventing integration outages with contract tests and canary releases

## Observability, Governance, and Operations
1. Creating API SLIs and SLOs that drive real reliability improvements
2. Tracing cross-service API requests with correlation IDs and distributed tracing
3. Designing audit-friendly APIs for compliance and regulated workloads
4. Rolling out breaking changes using deprecation windows and sunset policies
5. Defining API governance rules that improve consistency without slowing teams