Took me some time to figure out that Apache's mod_proxy actually requires the proxied service to be accessible when Apache itself starts.
It seems logical enough writing it down now, but when I was configuring mod_proxy to work with apt-cacher it sure wasn't clear looking at the log files.
So when you're playing around with mod_proxy and a random to-be-proxied service, make sure to reload/restart the service first (and verify everything working alright) and only then reload Apache to take the new mod_proxy settings into effect.
