Currently JIRA Data Center cluster nodes must have their RMI ports secured through the use of a firewall and or network segregation. However, as per https://docs.oracle.com/javase/8/docs/technotes/guides/rmi/rmi_security_recommendations.html, it is possible to run RMI over TLS/SSL where authentication is required for both the server and the client. In the future we should consider implementing authentication and TLS/SSL for RMI.