You can use Sun Cluster HA for Apache Tomcat in a multiple master configuration in the other scenarios. External load-balancing is required. A typical configuration uses the scalable Apache web server as a load balancer and configures one physical host name of an Apache Tomcat instance behind each instance of the Apache web server. Another option is to use a hardware load balancer, which handles the session context.
The difference between scalable and multiple masters configuration is only in the way, the clients access the cluster nodes. In a scalable configuration, they access the shared address. Otherwise the clients access the physical hostnames.