Table of Contents
Anyone can write a FastAPI "Hello World" endpoint. Few can build production systems that handle 20,000 requests per second. Here are interview questions that separate real FastAPI engineers from tutorial followers.
Dependency Injection Questions
Create a dependency that yields a session, close it in finally block. Use with or context manager. Ensure sessions don't leak.
Depends(func) passes the function; FastAPI caches result per request. Depends(func()) evaluates immediately - usually wrong.
Async & Concurrency Questions
asyncio.gather. Set timeouts. Handle partial failures gracefully (return_results=True).
Blocks the entire event loop. All other requests wait. Use run_in_executor or, better, async database driver.
System Design Questions
Strong candidates discuss async architecture, caching, database scaling, connection pools, observability, and failure handling.
Expect discussion around batching, queues, retries, autoscaling, and monitoring.
Pydantic & Validation Questions
Pydantic validator with custom validation. Or create dependency that queries database and raises HTTPException if not found.
Production & Scaling Questions
Check if sync code blocking event loop. Check database connection pool. Add timing middleware. Profile with py-spy or cProfile. Look for missing await.
Candidate Evaluation Guide
Async
What Strong Candidates Demonstrate:
Deep understanding beyond syntax
FastAPI
What Strong Candidates Demonstrate:
Dependency injection and lifecycle management
Databases
What Strong Candidates Demonstrate:
Pooling and performance optimization
Scaling
What Strong Candidates Demonstrate:
Load-testing and architecture experience
Operations
What Strong Candidates Demonstrate:
Monitoring and incident response knowledge
Test Real FastAPI Skills
FastAPI is easy to learn but hard to master. Hire engineers who understand async, dependency injection, and production deployment. Offline Pixel pre-vets FastAPI experts on these exact skills. Raise a request, talk to candidates, fund the project, and approve payment when you're satisfied.
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