Converged Application Server itself provides a multi-tier cluster architecture using Oracle Coherence. Coherence clusters consist of multiple managed Coherence server instances that distribute data in-memory to increase application scalability, availability, and performance. An application interacts with the data in a local cache and the distribution and backup of the data is automatically performed across cluster members.

Coherence integration aligns the lifecycle of a Coherence cluster member with the lifecycle of a managed server: starting or stopping a server Java Virtual Machine (JVM) starts and stops a Coherence cluster member. The first member of the cluster starts the cluster service and is the senior member.

Converged Application managed servers that are associated with a Coherence cluster are referred to as managed Coherence servers. Managed Coherence servers in each tier can be individually managed but are typically associated with respective Converged Application Server clusters.

A standard load balancing appliance is used to distribute traffic across the engines in the cluster. It is not necessary that the load balancer be SIP-aware; there is no requirement that the load balancer support affinity between Engines and SIP dialogs or transactions. However, SIP-aware load balancers can provide higher performance by maintaining a client's affinity to a particular engine.

Figure 4-1 shows an example Converged Application Server cluster in which traffic from the IP Network is routed through two load balancers, Load Balancer 1 and Load Balancer 2, which distribute requests to the four Converged Application Server engines in the clusters, Cluster 1 and Cluster 2. Within the same Coherence cluster a single Administration Server handles administration tasks for all of the Converged Application Server engines.