Recently we had to set-up a 3-node Galera Cluster with a Load Balancer in front of it. Because Galera Cluster nodes (mysqld) still reply to TCP requests on port 3306 when they are expelled from the Cluster it is not sufficient to just leave it to the Load Balancer to check the port if a Galera node is properly running or not.
We used the wsrep_notify_cmd variable to hook our own script into the Galera Cluster which disables each Node on the Load Balancer when its state changed.
# my.cnf
#
[mysqld] …
