"startup" and "shutdown" events not triggered for mounted APIs

[lazka]

Describe the bug

"startup" and "shutdown" events not triggered for mounted APIs

To Reproduce

from fastapi import FastAPI
from fastapi.testclient import TestClient

app = FastAPI()
subapp = FastAPI()
app.mount("/prefix", subapp)

@app.on_event("startup")
async def startup_event_1() -> None:
    print("startup for", app)

@app.on_event("shutdown")
async def shutdown_event_1() -> None:
    print("shutdown for", app)

@subapp.on_event("startup")
async def startup_event_2() -> None:
    print("startup for", subapp)

@subapp.on_event("shutdown")
async def shutdown_event_2() -> None:
    print("shutdown for", subapp)

with TestClient(app):
    pass

startup/shutdown is triggered for app but not subapp

Expected behavior

Events are emitted in both cases

[phy25]

Duplicate with #811.

[leonh]

on_startup and on_shutdown only triggered for the the top level app object. That is the expected behaviour in FastAPI.
These hooks are implementation of the ASGI spec provided by Starlette and not strictly part of FastAPI.
https://asgi.readthedocs.io/en/latest/specs/lifespan.html

[lazka]

That makes it hard to modularize the application though. At least on_event() should raise if the event can't be subscribed to.

What would be the downside of not making these events work on mounted apis?

[sm-Fifteen]

See encode/starlette#649, it's an upstream issue.

[lazka]

thanks. Anyway, closing in favor of #811 then

[tiangolo]

Thanks for coming back to close this one! ☕

Sorry for the long delay! 🙈 I wanted to personally address each issue/PR and they piled up through time, but now I'm checking each one in order.

[github-actions]

Assuming the original need was handled, this will be automatically closed now. But feel free to add more comments or create new issues or PRs.