Intermediate everything in Backend Dev, page 10
Rust references vs raw pointers
References are borrow-checked, always valid, aliasing-controlled, non-null; raw pointers carry no guarantees, can be null, dangling, or aliased, and dereferencing needs unsafe.
Concurrent TCP server: Go goroutines vs Rust std::thread
Both accept in a loop; Go spawns a goroutine per connection (go handle(conn)); Rust spawns an OS thread (thread::spawn moving the stream).
Rust async/await vs Go goroutines
Go schedules goroutines on a built-in runtime transparently; Rust futures are inert until polled by an external runtime like Tokio, and async colors functions.
Sharing mutable state: Go mutex vs Rust Arc Mutex
Go uses sync.Mutex by convention; Rust wraps data in Arc<Mutex<T>> so locking is mandatory, enforced by Send/Sync and the borrow checker.
Value versus pointer receivers and interface satisfaction
Value-receiver methods belong to both T and *T, but pointer-receiver methods belong only to *T, so a value of T may not satisfy an interface.
Rust borrow rules versus Go race prevention
Rust's aliasing-XOR-mutability rule plus Send and Sync make races a compile error; Go prevents them at runtime via channels, mutexes and the race detector.
Rust binary and library crates in one project
A binary crate has main and produces an executable; a library crate has lib.rs and is reusable; put logic in the lib and a thin main that calls it.
Explain multi-stage Docker builds for Python and builder vs runtime
Tests separation of build-time and runtime concerns. A strong answer contrasts the builder stage (gcc, headers, wheels) with the runtime stage (slim base, copied artifacts, no compiler). Red flag: citing size alone while ignoring security and caching.
How do you manage configuration and secrets for a containerized FastAPI app?
Tests 12-factor config separation and Docker secret hygiene. A strong answer uses pydantic-settings with runtime env vars, lru_cache, and keeps .env out of the image. Red flag: baking credentials into Dockerfile layers or committing .env files.
What are the key responsibilities for Nginx versus Uvicorn?
This tests the reverse-proxy versus ASGI-server boundary. A strong answer gives Nginx TLS termination, static files, buffering, and load balancing, while Uvicorn runs the Python app and async workers.
How do you authenticate a FastAPI WebSocket connection?
This tests WebSocket limits and FastAPI dependency injection. Pass the JWT via query parameter or cookie at handshake, validate it with Depends, and reject with HTTP 403 or 1008 close.
Use startup events to initialize a database pool and inject it
This tests FastAPI lifespan hooks and dependency injection for shared state. A strong answer creates the pool in an async startup handler, stores it on app.state, and accesses it via a dependency in routes. A red flag is creating a fresh pool per request.
How do you handle a WebSocket client disconnect in FastAPI?
Cite installing websockets, Handling disconnections and multiple clients pattern, and Depends.
How do you mark a FastAPI endpoint as deprecated?
Mark a FastAPI route with deprecated=True on its path operation decorator. FastAPI emits the OpenAPI deprecated flag, which Swagger UI can display; this metadata does not remove or disable the route.
How do you group FastAPI endpoints under tags and describe groups?
Tests FastAPI's two-step tag system: decorators label routes, and openapi_tags supplies group descriptions. Good answers cover tagging paths with tags=["users"], then defining metadata in FastAPI(openapi_tags=[...]) with matching names.
How can you provide a Swagger UI example for a Pydantic body?
Tests whether you know FastAPI generates OpenAPI schema from Pydantic metadata. A strong answer names Field(example=...) for per-field samples and Body(example=...) for the full payload.
How do you document multiple response schemas in OpenAPI?
This tests FastAPI OpenAPI schema generation for error responses. A strong answer covers the decorator responses dict mapping status codes to Pydantic models and descriptions, plus manually returning JSONResponse with that code.
How would you use pytest fixtures to manage TestClient and mock dependencies?
Tests FastAPI test isolation and dependency overrides. Strong answer: function-scoped fixture yielding TestClient, mock injection via app.dependency_overrides, and teardown cleanup to prevent state leaks.
How do you test a FastAPI endpoint without real tokens?
Tests whether you know FastAPI's dependency override mechanism to isolate business logic from auth. A great answer describes using app.dependency_overrides to swap the auth Depends for a mock returning a fake user, then cleaning up after the test.
Explain FastAPI dependency overrides with an in-memory SQLite test example
This tests FastAPI's hook for swapping dependencies cleanly in tests. A strong answer names app.dependency_overrides, defines a test-only in-memory SQLite session, and handles teardown. A red flag is patching globals or mocking ORM instead of dependency.
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