After fighting apache for a couple hours, I finally have mongrel set up to proxy through apache.
At first I had the proxy module enabled but was getting a 403 page. After adding logging to the vhost config, I see
[Mon Sep 10 22:57:00 2007] [warn] proxy: No protocol handler was valid for the URL /. If you are using a DSO version of mod_proxy, make sure the proxy submodules are included in the configuration using LoadModule.
I go ahead and find out I didn’t have proxy_http enabled. After executing
sudo a2enmod proxy_http and bouncing apache, TA-DA!