Why use an ASGI server like Uvicorn instead of the dev server?

WHAT THIS TESTS: This question checks whether you understand the distinction between development and deployment environments for a FastAPI application. An interviewer wants to see that you know deployment means making an application available to users on a remote machine with a server program that delivers good performance and stability, rather than treating the development server as sufficient for real traffic.

A GOOD ANSWER COVERS: First, define Uvicorn as a production server program used to run the application. Second, describe the development server as a tool built for a workflow of constant code changes, breaking, fixing, and stopping or restarting frequently. Third, contrast this with production needs where users require efficient access without interruptions or problems, which means the server must provide performance and stability. Fourth, note that deployment involves placing the application on a remote machine and choosing a strategy that fits your use case, but the core requirement is moving away from the development server to a proper production server program.

COMMON WRONG ANSWERS: Saying Uvicorn is only needed for async support without mentioning stability or uninterrupted access. Claiming the development server is fine for small or internal production workloads. Describing deployment as simply copying code to a server without discussing the server program that provides performance and reliability. Conflating the convenience of local hot reloading with the robustness required for user facing services.

LIKELY FOLLOW-UPS: How do you handle multiple worker processes with Uvicorn in production? What deployment strategies exist beyond running a server manually? How would you containerize this application while maintaining the same production server requirements? What steps would you take to add HTTPS in a production deployment?

ONE CONCRETE EXAMPLE: Imagine you have built a FastAPI API locally using the development server. When you deploy it, you move the application to a remote machine and use Uvicorn as the server program. You choose Uvicorn because the development server is designed for a cycle of constant changes, breaking, and restarting, which would interrupt your users. In production, Uvicorn provides the performance and stability needed so customers can access the API efficiently and without problems.