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"@context": "https://schema.org",
"@type": "BlogPosting",
"headline": "Advanced API Design Patterns",
"description": "A deep-dive into production-ready API design patterns every senior engineer should know, covering versioning strategies, cursor-based pagination.",
"datePublished": "2026-03-20",
"author": {
"@type": "Organization",
"name": "CodeSwiftr Team"
},
"url": "https://codeswiftr.com/blog/api-design-advanced-patterns"
}
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"@context": "https://schema.org",
"@type": "FAQPage",
"mainEntity": [
{
"@type": "Question",
"name": "What are the most important API design patterns every senior engineer should know?",
"acceptedAnswer": {
"@type": "Answer",
"text": "Senior API design patterns that appear in interviews: Idempotency Keys (making POST operations safe to retry by keying on a client-provided UUID), Optimistic Concurrency Control using ETags (prevent lost updates when multiple clients edit the same resource), the Outbox Pattern (write to a database outbox table in the same transaction as business logic, then publish events from the outbox — guarantees events are published if and only if the transaction commits), Long-Running Operation Pattern (return 202 Accepted with a polling URL for operations that take minutes, checking status at GET /operations/{id}), and Bulk Operations (POST /users/batch for efficient multi-entity mutations to avoid N sequential API calls). Demonstrating familiarity with these patterns beyond basic CRUD signals real production API experience."
}
},
{
"@type": "Question",
"name": "How does optimistic concurrency control work in REST APIs?",
"acceptedAnswer": {
"@type": "Answer",
"text": "Optimistic concurrency control (OCC) prevents lost updates when multiple clients try to modify the same resource simultaneously. Implementation: GET /users/123 returns the resource with an ETag header (a hash of the resource state, e.g., ETag: \"abc123\"). The client includes If-Match: \"abc123\" in their PATCH or PUT request. The server checks whether the current resource state matches the provided ETag — if it does, the update proceeds and a new ETag is returned; if it doesn't (another client modified the resource in the meantime), the server returns 412 Precondition Failed. The client must re-fetch the resource, merge changes, and retry. OCC is preferred over pessimistic locking for APIs because it avoids lock contention and distributed lock management. It works well when concurrent edits to the same resource are rare."
}
},
{
"@type": "Question",
"name": "What is the API Outbox Pattern and why does it matter for event-driven systems?",
"acceptedAnswer": {
"@type": "Answer",
"text": "The Outbox Pattern solves the dual-write problem: you need to both update your database and publish an event to a message broker (Kafka, RabbitMQ, SQS), but these two writes cannot be made atomic in a distributed system. If you write to the database then crash before publishing the event, the event is lost. If you publish the event then crash before writing to the database, you have an event with no corresponding data change. The solution: write a record to an 'outbox' table in the same database transaction as your business logic update. A separate process (the 'outbox worker' or Debezium CDC connector) reads the outbox table and publishes events to the broker, then marks them as published. This guarantees exactly-once event publishing from a single database transaction. It is foundational knowledge for senior backend and distributed systems interviews."
}
},
{
"@type": "Question",
"name": "How should APIs handle long-running operations that take minutes to complete?",
"acceptedAnswer": {
"@type": "Answer",
"text": "Long-running operations should use the Asynchronous Request-Reply pattern. Step 1: client sends POST /reports/generate, server immediately returns 202 Accepted with a Location header pointing to a polling endpoint: Location: /operations/op-789. Step 2: client polls GET /operations/op-789, which returns {status: 'pending', progress: 45} until complete. Step 3: when complete, GET /operations/op-789 returns {status: 'complete', result_url: '/reports/result-789'} or includes the result directly if small. Alternatives: WebSocket connection for real-time progress updates (better for interactive UIs, more complex to implement), Server-Sent Events (SSE) for one-way streaming progress updates (simpler than WebSocket for progress notifications). Webhooks are appropriate when the client is a server and can receive HTTP callbacks — POST the result to a client-provided callback URL when complete."
}
}
]
}