memcached – What cdn or cache modifies max-age dynamically as content ages?

I am trying to determine what is caching web page responses within the server infrastructure in a transparent cache like behaviour.

The cache header defined by the origin server is fixed one hour (3600).

When a standard browser request is made without a cache control header in the request, we are seeing cached output and a modified cache-control header in the response:

cache-control: public, max-age=3421

Cloudfront is involved but configured to not cache this page. In the same response we also see

x-cache: Miss from Cloudfront

If a refresh request is made by the browser which adds cache-control:none to the request header, we then see fresh content from the server and the max-age is back to 3600.

Based on this behaviour with the max-age appearing to ‘count down’ over time, is it possible to determine what application or system is caching content? There should not be a cache enabled.

Possible systems involved include appDynamics and f5 big-ip