Hello!
On Sun, Apr 07, 2024 at 04:56:20PM +0300, Maxim Dounin wrote:
> On Sun, Apr 07, 2024 at 01:36:21PM +0200, Kirill A. Korinsky wrote:
>
> > Greetings,
> >
> > Let assume that I would like behavior on LB from the backend and force it to
> > cache only resposnes that have a X-No-Cache header with value NO.
> >
> > Nginx should cache a response with any code, if it has such headers.
> >
> > This works well until the backend is unavailable and nginx returns a
> > hardcoded 502 that doesn't have a control header, but such a response is
> > cached anyway.
> >
> > Here is the config that allows to reproduce the issue:
> >
> > http {
> > default_type application/octet-stream;
> >
> > proxy_cache_path /tmp/nginx_cache keys_zone=the_zone:1m;
> > proxy_cache the_zone;
> > proxy_cache_valid any 15m;
> > proxy_cache_methods GET HEAD POST;
> >
> > add_header X-Cache-Status $upstream_cache_status always;
> >
> > map $upstream_http_x_no_cache $no_cache {
> > default 1;
> > "NO" 0;
> > }
> >
> > proxy_no_cache $no_cache;
> >
> > upstream echo {
> > server 127.127.127.127:80;
> > }
> >
> > server {
> > listen 1234;
> > server_name localhost;
> >
> > location / {
> > proxy_pass http://echo;
> > }
> > }
> > }
> >
> > when I run:
> >
> > curl -D - http://127.0.0.1:1234/
> >
> > it returns MISS on the first request, and HIT on the second one.
> >
> > Here I expect both requests to return MISS.
>
> Thanks for the report.
>
> Indeed, proxy_no_cache is only checked for proper upstream
> responses, but not when caching errors, including internally
> generated 502/504 in ngx_http_upstream_finalize_request(), and
> intercepted errors in ngx_http_upstream_intercept_errors().
>
> Quick look suggests there will be also issues with caching errors
> after proxy_cache_bypass (errors won't be cached even if they
> should), as well as issues with proxy_cache_max_range_offset after
> proxy_cache_bypass (it will be ignored).
>
> This needs cleanup / fixes, added to my TODO list.
I've posted a patch to address proxy_no_cache issues along with
relevant tests here:
https://freenginx.org/pipermail/nginx-devel/2024-June/000382.html
https://freenginx.org/pipermail/nginx-devel/2024-June/000383.html
Please take a look if it works for you.
--
Maxim Dounin
http://mdounin.ru/
