Migration Guide: JGroups now default to a "private" network interface, which is new in EAP 7

In JBEAP-3836, we added information to the Config Guide that "By default, JGroups only binds to the localhost network interface". More specifically, it binds to the private interface as defined in server configuration.

This is a change compared to EAP 6, where the server configuration didn't contain any such "private" interface and JGroups bound by default to the "public" interface. This change is a move towards a recommended practice and I think many customers already used a configuration with a dedicated interface for clustering communication, but we should mention it anyway.

I imagine a new subchapter under 4.4. Clustering Configuration Changes that will say something like:

In default EAP 6 configuration, JGroups used the public interface from the <interfaces> part of server configuration. Recommended practice is to use a dedicated network interface, which also required defining a new interface in the server configuration. EAP 7 provides that dedicated interface in the server configuration by default, it's called private. JGroups now use that interface by default.

And a link to chapter 18.2.2. Binding JGroups to a Network Interface in the Config Guide (I expect it to stay, it should just be shorter.)