[Python] FastAPI lifespan does not work when running with docker

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 hostort (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.

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