mod_perl output filter and mod_proxy, mod_cache

Hi,

Is it in theory possible to insert a perl output filter between 
mod_proxy and mod_cache?

Or at least between mod_proxy and the client?



The problem I'm trying to solve is this:

We have 100+ web servers where apache fronts a separate tomcat server 
using mod_proxy.

Sadly, the tomcat dev's forgot to set any caching headers in the HTTP 
response (either Expires, Last-Modified or Cache-control) so the sites 
are largely uncacheable by browsers and the various tomcats are becoming 
overloaded.

1/3 of our sites are typically invariant (the production sites have 
stable and unchanging data and most queries are via GET requests).

Therefore, the idea of forcing in some cache control headers en-route 
and also enabling some apache caching has a good chance of working well 
without affecting anything.

mod_headers and mod_proxy don't seem to play well together and mod-cache 
doesn't either (probably due to lack of cache control headers in the 
tomcat response, though I haven't proved this is actually the case).

So the thought of doing a perl based filter to insert cache-control 
headers occurred.

It is likely I can insert such a filter on Apache 2.2 *between* 
mod_proxy and mod_cache?

Or am I going to have to implement a filter that includes proxying 
and/or caching?

Many thanks for any advice,

Cheers,

Tim

-- 
Tim Watts
Personal Blog: http://www.dionic.net/tim/