How important is the "reuseport" flag for quic?

[J Carter]

Hello,

On Sat, 15 Jun 2024 13:58:55 +0100
Dominic Preston <lzqhwo at gmail.com> wrote:

> I'm using nginx 1.26.1 from the nginx.org ubuntu repo.
> 
> I find when I remove the "reuseport" flag from the "listen" directive
> for my quic port, a lot page assets fail to load, and the browser
> ultimately falls back to http/2.
> 
> When I re-add "reuseport", all http/3 requests succeed again.
> 
> How crucial is "reuseport" when using quic on nginx? Is it normal for
> things to break badly without it?
> _______________________________________________

Very, it's required to use the reuseport parameter when using multiple
workers as per the documentation here[1] so that all UDP packets of a
HTTP/3/quic connection are routed to and handled by the same worker, as
I understand. 

This is just due to limitations of how UDP (being
stateless and sessionless) is handled by the kernel compared to TCP
(which is session orientated).

[1] https://nginx.org/en/docs/quic.html#configuration