The load-balancing is done by serving the JNLP file from different servers when the Apache HTTP front-end is accessed. Add to each of the Servoy Application Server's "servoy.properties" files the following line (needed for Smart Client load balancing):

servoy.jnlpCodebaseOverride=http://thisServersHostnameAsSeenByClients:port
What you should also take into consideration when setting up a load-balanced cluster, is allowing smart-clients to connect directly to individual servers in the cluster. This means that all Servoy Application Servers should be accessible from the client side - and you might want to isolate the cluster so that connections to ports used by Terracotta (see tc-config.xml) are only allowed from within the cluster, even if connections from client machines on Servoy ports should be allowed to all Servoy Application Servers.