Nginx unexpectedly returning 304 for content cached from proxy

[Igor Sysoev]

On Mon, Jun 08, 2009 at 01:39:12PM +0400, Antonio L. wrote:

> Hello!
> We recently started using Nginx 0.7.59 to replace Squid on a couple of our
> static file caching servers (Debian 5.0). However, nginx is returning "HTTP
> 304 Not Modified" responses for some?not all?of the cached images, even if
> the browser doesn't send an If-modified-since header -- causing lots of
> broken images when viewing the site in browser.
> 
> As soon as I turn off the "proxy_cache" directive and let the requests be
> proxied to the upstream server, bypassing nginx's cache, no more unexpected
> 304's are served, and the broken images disappear.
> 
> Do you have any idea of what might be causing this problem?
> 
> My nginx.conf file is below:
> 
> ###
> worker_processes  3;
> 
> error_log  logs/error.log;
> 
> events {
>     worker_connections  10240;
>     use epoll;
> }
> 
> http {
>     include       mime.types;
>     default_type  application/octet-stream;
> 
>     access_log  off;
> 
>     sendfile        on;
>     keepalive_timeout  10;
> 
>     gzip  on;
> 
>     upstream backend {
>         server  xxx.xxx.xxx.xxx;
>     }
> 
>     proxy_buffer_size 16k;
>     proxy_buffers 8 16k;
>     proxy_busy_buffers_size 32k;
>     proxy_intercept_errors on;
>     proxy_cache_path /var/www/cache levels=1:2
>             keys_zone=zone_one:10m inactive=24h;
> 
>     server {
>         listen       80;
>         server_name  localhost;
> 
>         location / {
>             proxy_cache zone_one;
>             proxy_cache_valid 200 7d;
>             proxy_pass http://backend;
>         }
>     }
> }
> ###

This is a bug. I will try to fix in today 0.8.1.
As quick workaround, you may set any proxy_set_header directive in
cached location, e.g.:

         location / {
             proxy_cache zone_one;
             proxy_cache_valid 200 7d;
             proxy_pass http://backend;
+            proxy_set_header  Host  backend;
         }


-- 
Igor Sysoev
http://sysoev.ru/en/