Simple way
Ensure certain traffic goes to a certain server (master), you can use this:
sh
<LocationMatch "^/wordpress/wp-admin/?.*>
ProxyPreserveHost On
ProxyPass http://ip.of.master.server/
</LocationMatch>
For a better setup with Variables, just follow the... following steps :)
Step One: Configure Environment
We need to setup some environment variables to get this to work correctly.
Add the following to your environment on the slave server(s):
RHEL/CentOS: /etc/sysconfig/httpdi
sh
OPTIONS="-DSLAVE"
export MASTER_SERVER="SERVERIP HERE"
Ubuntu: /etc/apache2/envvars
sh
export APACHE_ARGUMENTS="-DSLAVE"
export MASTER_SERVER="SERVERIP HERE"
Step Two: Configure your VirtualHost
In your VirtualHost configuration do something like the following.
sh
<IfDefine SLAVE>
RewriteEngine On
ProxyPreserveHost On
ProxyPass /wp-admin/http://${MASTER_SERVER}/wp-admin/
ProxyPassReverse /wp-admin/http://${MASTER_SERVER}/wp-admin/
RewriteCond %{REQUEST_METHOD} =POST
RewriteRule . http://${MASTER_SERVER}%{REQUEST_URI} [P]
</IfDefine>