Kovid, I can easily see your point. However, you are describing a different use case, i.e. lots of and frequent requests. @DouglasK and I have a different use case: very rare requests, almost guaranteed not to be simultaneous, where it would be advantageous if the calibre server would not be loaded all the time. Therefore, I think your initial architectural decision to provide both must be applauded. I also understand that you are hesitant to support the inProcess approach - it requires the distro (not binary) version, and those are notoriously behind the latest revision. At any rate, apache 2.4 broke both approaches the way they are described in the docs. While I had no luck with the inProcess version, I could get the reverse Proxy to work. Here is how (YMMV):
LoadModule proxy_module /usr/lib/apache2/modules/mod_proxy.so
LoadModule proxy_http_module /usr/lib/apache2/modules/mod_proxy_http.so
ProxyPass /calibre
http://localhost:8080/calibre
ProxyPassReverse /calibre
http://localhost:8080/calibre
SetEnv force-proxy-request-1.0 1
SetEnv proxy-nokeepalive 1