Configuring apache virtual hosts for one domain and multiple IP addresses - apache

Question

I have two apache servers at two separate IP addresses and one domain name (example.com) administer on godaddy.com. I want to use this single domain to point traffic to my two separate servers over ssl.
I set up the first server through a fios router with port forwarding and associated the public IP address with a DDNS address (xxx.ddns.net). My godaddy config looks like this:
Type Name Value
-------------------------------
A # 184.168.131.241
CNAME www xxx.ddns.net
Forwarding
------------
domain https://www.example.com
... and my apache ssl.conf file looks like this:
<VirtualHost *:443>
...
ServerName www.example.com
DocumentRoot /var/www/html
</VirtualHost>
This works fine, but now I want to set up a subdomain ('mysub') so that traffic directed to mysub.example.com gets handled by my second server available at a separate IP address (MY.2ND.IP.ADDR). I've tried all sorts of settings on godaddy and in the ssl.conf file, but to no avail. In particular, I've tried:
Setting godaddy so that traffic sent to subdomain mysub.example.com is redirected straight to MY.2ND.IP.ADDR; it's not at all clear to me if this is possible. (Godaddy has a form under the title "Forwarding" and a subsection therein called "subdomain", but setting that subdomain to mysub and setting "forward to" to http://MY.2ND.IP.ADDR doesn't seem to do anything; what is this 'subdomain' field in the godaddy interface supposed to be used for?)
Directing all traffic to the first server, and configuring apache to proxy traffic for the subdomain on to the second server.
I've tried adding another virtual host element to ssl.conf like so:
<VirtualHost MY.2ND.IP.ADDR:443>
ServerName mysub.example.com
<Proxy *>
Order deny,allow
Allow from all
</Proxy>
<Location />
ProxyPass http://MY.2ND.IP.ADDR
ProxyPassReverse http://MY.2ND.IP.ADDR
</Location>
</VirtualHost>
... but this doesn't work either.
In summary, what is the best way to direct traffic for a subdomain to a separate IP address using godaddy and/or apache configurations?