Am I using proxy_cache correctly?

Server NGINX
1

Hi all,

I’m trying to make sure that I have my disk caching set up properly for
a specific subdomain under nginx. Here’s what I have in my nginx.conf:

proxy_cache_path /opt/nstein/cache levels=1:2 keys_zone=CACHE:100m

inactive=10m max_size=1g;
proxy_temp_path /opt/nstein/cache/tmp;

And here’s what I have in my site config file:

server {
server_name media.domain.com;
access_log off;

location / {
    proxy_pass      http://nstein_mm-rest_cluster;
    proxy_cache     CACHE;
    proxy_cache_valid       200 10;
    proxy_cache_valid       404 1m;
    proxy_cache_key "$host$request_uri";
    proxy_cache_use_stale   error timeout invalid_header;;
}

}

Basically it’s image requests that come through media.domain.com, but we
are using GD to perform image resizing. For instance, requests like
this are sent through:
http://media.domain.com/?controllerName=image&action=get&id=4164&format=homepage_lead

I can see the image binary data in my /opt/nstein/cache directory and
nginx does seem to be serving from cache correctly. What’s odd to me is
that if I run ab (Apache benchmark) against the above URL, I’ll still
see some of the requests passed on to the back end Apache server,
however most of the time the request is served from cache.

Is there a reason that some of the requests are still passed to back
end? Why is it that not all are served from cache?

Thanks!

Posted at Nginx Forum: