gunicorn --reload doesn't work with Uvicorn workers. Bug?

[gwerbin]

I have a trivial FastAPI application in hello.py:

from fastapi import FastAPI

app = FastAPI()

@app.get('/')
async def hello():
    # return "hello!"
    return {"msg": "hello!"}

I am running this using Gunicorn with Uvicorn workers as follows:

gunicorn --reload --worker-class 'uvicorn.workers.UvicornWorker' 'hello:app'

You can make requests to this server using curl http://localhost/ and you should see a JSON response.

When I make a change to hello.py (e.g. swapping the commented-out lines), the Gunicorn log output indicates that a change was detected and that the server was reloaded. However, checking with curl indicates that the app was not actually reloaded; the response does not change.

When I run directly with Uvicorn, reloading works fine:

uvicorn --reload 'hello:app

Is this a Gunicorn bug, a Uvicorn bug, or a "known-bad" interaction?

I am happy to use uvicorn directly instead of gunicorn for development purposes if this is something that can't be fixed. But I am still curious about this issue.

[Kludex]

Kind of a bad already known interaction. Currently, the Uvicorn worker doesn't reload with gunicorn. Use Uvicorn standalone for development.

I'm unable to post references for now, but I have a closed PR with this fix I think.

[iudeen]

May be this? #1193

[Kludex]

Yes

[gwerbin]

Use Unicorn standalone for development.

Good to know and thank you for the quick answer. Maybe this is worth mentioning explicitly in the docs.