I have succeed in clustering geoserver on windows using three Apache tomcat instances and Apache server as load balancer. I also shared the data directory but I have two issues:
when I try to login in the geoserver through the load balancer, I failed to login although the username and password are correct and I didn't get any error message. And when I logged in geoserver through any instance of tomcat, the geoserver through the load balancer didn't login.
when I upload a layer on an instance of geoservers, the others didn't sync until I reload the configuration of each one.