Codebeamer uses Ehcache as a framework for distributed cache replication, leveraging RMI (Remote Method Invocation) to synchronize cache data across the cluster. For this communication to function, ports 4001, 4002, and 9000 must be opened between cluster nodes. However, these ports should not be accessible from the public internet to ensure security.

In Codebeamer, a single RMI service is responsible for communicating with all nodes in the cluster, calling them one by one to ensure proper synchronization and data consistency.