The cluster need to maintain a list of current member nodes at all times so that the load balancer and client interceptor know how to route their requests. The discovery protocols are used to discover active nodes in the cluster. All initial nodes are discovered when the cluster starts up. When a new node joins the cluster later, it is only discovered after the group membership protocol (GMS, see Section 2.1.5.1, “Group Membership”) admits it into the group.

Since the discovery protocols sit on top of the transport protocol. You can choose to use different discovery protocols based on your transport protocol. The discovery protocols are also configured as sub-elements in the JGroups MBean Config element.