What happens if my startup code crashes?

If the code before the `yield` throws an exception, FastAPI will completely abort the boot sequence. Uvicorn will exit with an error, and the server will never open its port to accept HTTP requests. This is a good thing; it prevents broken servers from going live.

Can I do async work inside the lifespan?

Yes, the lifespan function is defined with `async def`. This means you can use `await` to establish async database connection pools or fetch configuration files from an external API during boot.

Is it safe to store database connections in app.state?

Yes, it is extremely common to store the global database engine or connection pool in `app.state` during the lifespan, and then have your request-level dependencies pull from that pool.

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Lifespan Events

Master FastAPI Lifespan events. Learn how to use async context managers to execute heavy startup tasks, safely close down resources during termination, and share global state across your endpoints.

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