FastAPI lifespan does not work when running with docker

Question

My app with lifespan defined like this:

@contextlib.asynccontextmanager
async def lifespan(app:fa.FastAPI):
    print("LIFE SPAN: Start up")
    yield
    print("LIFE SPAN: Shutdown")
app_api = fa.FastAPI(lifespan=lifespan)

app_api.include_router(test.router)

inside retrofun/___main___.py .

from retrofun.api import app_api
import argparse
import uvicorn

def main():
    parser = argparse.ArgumentParser(
        description="Run the RetroFun application.")
    parser.add_argument(
        "-p", "--host-port", type=str, default="localhost:8000",
        help="Specify the host and port with format host:port (default: localhost:8000)")
    args = parser.parse_args()

    host,port=args.host_port.split(':')
    port = int(port)
    print(f"Starting retrofun at {args.host_port} ...")
    uvicorn.run(
        "retrofun.__main__:app_api",
        host=host,
        port=port,
        reload=True
    )

if __name__=="__main__":
    main()

Case 1: When I run python -m retrofun. Everything including lifespan works well.

Case 2: With docker file:

CMD ["uv","run","-m","retrofun","-p","0.0.0.0:5555"]

Everything works well like intent EXCEPT lifespan does not work (print to console) anymore.

Case 3: If i change the CMD in Dockerfile with another like:

CMD ["uv","run","fastapi","run","./src/retrofun/__main__.py"]

Lifespan works again.

Question: Why lifespan does not work in case 2 and how to resolve that? Thank you.

Jordan · Accepted Answer · 2025-03-10 00:52:11Z

0

Try removing reload=True as the reload mechanism works by killing and restarting child processes. The lifespan startup/shutdown hooks are tied to the child processes, not the main process.

Also try running

CMD ["uv", "run", "retrofun.main:app_api", "--host", "0.0.0.0", "--port", "5555"]

instead of

CMD ["uv","run","-m","retrofun","-p","0.0.0.0:5555"]

because it directly tells uvicorn to import app_api as the FastAPI instance.

answered Mar 10 at 0:52

Jordan

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