Uvicorn can be run without installing gunicorn

[Simon Willison]

​https://docs.djangoproject.com/en/4.1/howto/deployment/asgi/uvicorn/ currently says you should do this:

python -m pip install uvicorn gunicorn

Then:

gunicorn myproject.asgi:application -k uvicorn.workers.UvicornWorker

This isn't actually necessary: you can install just uvicorn and then do this:

uvicorn myproject.asgi:application

[Mariusz Felisiak]

This was added in c1442e1192057a3bf14aecbaa1b713eee139eaff, see ​PR.

[Simon Willison]

Huh, that's surprising. I've been deploying Uvicorn apps for a few years now without using gunicorn at all.

​https://github.com/django/django/pull/13455 seems to have made that decision based on the Uvicorn docs themselves at ​https://www.uvicorn.org/deployment/#gunicorn - which do recommend gunicorn for production, but don't explain why.

I'm going to try and work out WHY they recommend gunicorn, and maybe suggest a change to the Django docs that helps make that clear.

[Simon Willison]

It looks like the recommendation to use gunicorn with uvicorn dates back to this commit four years ago: ​https://github.com/encode/uvicorn/commit/07c6c18945ab4f4167118e717e197adce3aee3da#diff-b4d68dc855d0f9476d3f2ee343853bd21bf82ea9960d0cf06661baa244439dd6R93-R111 - and prior to that fix gunicorn was baked into uvicorn itself.

[Simon Willison]

Best answer I've found so far is this comment by Tom Christie: ​https://github.com/encode/uvicorn/issues/303#issuecomment-464154975

So: Gunicorn will give you multiple worker processes, as well as monitoring and restarting any crashed processes. We might start to have some of those things built directly into Uvicorn at some point, but for now if you want multiple processes you need to use Gunicorn or some other process manager such as circus.

[Simon Willison]

The FastAPI deployment documentation talks about reasons to use Gunicorn here: ​https://fastapi.tiangolo.com/deployment/server-workers/

[Simon Willison]

There's an interesting draft PR against Uvicorn here which updates their deployment documentation to reflect current recommendations.

​https://github.com/encode/uvicorn/pull/1607/files

One of the new points in there is the idea that gunicorn isn't necessary if you are deploying inside a container - where using uvicorn alone works fine.

But... that PR is still being discussed. I don't think the advice there is stable and agreed upon yet.

[Simon Willison]

The title of the page at ​https://docs.djangoproject.com/en/4.1/howto/deployment/asgi/uvicorn/ is "How to use Django with Uvicorn".

As such, I think it's worth explaining both the with-gunicorn and without-gunicorn mechanisms. I'll update my PR to do that instead.

[Simon Willison]

Updated my PR to add the Gunicorn content back in as a separate section: ​https://github.com/django/django/pull/16199/commits/ab2b704f652ecde718cf32d4b1e441a4087e92f1

[Simon Willison]

Just talked to Andrew Godwin about this. He confirmed that Gunicorn isn't necessary when running applications in a container environment which features a separate layer that handles automatic restarts on failure, such as Kubernetes.

[GitHub <noreply@…>]

In 022a864a:

Fixed #34109 -- Updated instructions for running with Uvicorn.

Co-authored-by: Paolo Melchiorre <paolo@…>

[Carlton Gibson <carlton.gibson@…>]

In ccb830e2:

[4.1.x] Fixed #34109 -- Updated instructions for running with Uvicorn.

Co-authored-by: Paolo Melchiorre <paolo@…>
Backport of 022a864a5d1de28b853f009566a24be251e90d96 from main