Galera provides a set of status variables, which can be used to monitor the status of each node. Like Galera server variables, each status variable starts with the 'wsrep_'
prefix. This allows visualizing all the variables easily with the following query:
SHOW STATUS LIKE 'wsrep%';
There are at least two ways to automate the monitoring of MariaDB Galera Cluster:
Using a plugin called Galera Cluster Nagios. It is developed and maintained by FromDual, and can be downloaded from their site: http://www.fromdual.com/. This plugin is not covered by this book. The FromDual's website provides the needed documentation.
Using Galera automatic notifications.