Why JBoss EAP worker nodes fail to use the right hostname on mod_cluster?

Issue

• If there are Apache httpd proxies running on the same nodes as JBoss servers, then each EAP worker node only connects to the Apache httpd proxy that runs on its local machine, it does not connect to other proxies of the cluster. Otherwise, all JBoss worker nodes fail to join mod_cluster and JBoss server.log shows the message:

  2018-08-13 20:37:45,845 ERROR [org.jboss.modcluster] (UndertowEventHandlerAdapter - 1) MODCLUSTER000043: Failed to send INFO command to localhost/127.0.0.1:6666: Connection refused (Connection refused)