Apache: Reverse proxy the whole domain

ProxyPass is very nit-picky about slashes; since you're proxying a trailing slash (just the root, /), you'll want to proxy TO a trailing slash.

So, adding some trailing slashes to your targets, as below, should help out.

Also, since the device you're proxying too is the local system, you may want to avoid potential name resolution/NAT confusion by using 127.0.0.1. What you place here has no bearing on the host header received by the server, and the client header is passed through, as long as you've got ProxyPreserveHost On set:

ProxyPreserveHost On
ProxyPass / http://127.0.0.1/host2/
ProxyPassReverse / http://127.0.0.1/host2/

If that doesn't work, prehaps have host2 serve up some temporary content page to verify that you're hitting the correct vhost.

Side note, you don't want that <Proxy *> block. It's built for when you're running in ProxyRequests on mode, and doesn't work as desired for reverse proxies (use <Location> instead for access control)