Re: mod_perl output filter and mod_proxy, mod_cache

And here is another link which might be interesting.
It is a message on the Tomcat list (where I re-posted your original request, hem), from
Rainer Jung, who is one of the Apache/Tomcat mod_jk connector developers :

"
Yes, go for TC 7:

http://tomcat.apache.org/tomcat-7.0-doc/config/filter.html#Expires_Filter

Regards,

Rainer
"

Now that Tomcat page, apart from its own interest, also points to the Apache "mod_expires" 
module (which I never heard about before) in your case may be exactly what you're looking for.

It seems to be such that it can add headers in a response proxied to Tomcat, without 
overwriting such headers if they already exist.


Here is what I would do :

1) identify some "usual suspects" among the URLs proxied to Tomcat
    They would have to match the following criteria :
    - they happen on an overloaded Tomcat
    - they happen often
    - I am reasonably sure that the information delivered by that URL
      is stable over a period of time
    - I am reasonably sure that if it happened that the browser would,
      once in a while, get stale information, it would not be dramatic

2) carefully configure the front-end Apache to, for these particular URLs,
add an Expires header specifying "now + N", where N is initially not too large.
This way, a browser would not get a result that is more than N outdated, but any duplicate 
request within a period N would get the cached version.

3) look at the impact and loop or not, increasing or decreasing N

YMMV.