When using TCPPING for discovery, if the very first attempt to discover the rest of the cluster fails (in my case, the connections are timing out due to a suspected EC2 issue), the new node decides that it is alone in the cluster and creates a new view of just itself.

Later, when performing periodic discovery, the new node successfully connects to the existing cluster and sends a GET_MBRS_REQ but, since it's already in a view (the one where it's alone), it doesn't fill in its local IP address (see the logic or this at https://github.com/belaban/JGroups/blob/master/src/org/jgroups/protocols/Discovery.java#L254). This means that the old nodes in the cluster cannot send a reply or any other cluster messages to the new node. Thus the new node, which never get a response to its GET_MBRS_REQ, continues to think it's alone in the world and the old members, who got a record of a new cluster member but no address to communicate with it on, start logging that they're dropping messages to <UUID> because they have no physical address. The cluster never heals.

If the physical address were included in all GET_MBRS_REQ messages (e.g. if the if statement were removed from the file I linked above), then, even if initial discovery fails, future discovery would succeed and the cluster would heal itself.

This is a superficially similar issue to https://issues.jboss.org/browse/JGRP-1203, but, in that case, the cluster will heal once A performs a discovery later while in this one it never heals.