This functionality enables repmgrd (when running on the primary) to
monitor connected child nodes. It will log connections and disconnections
and generate events.
Additionally, repmgrd can execute a custom script if the number of connected
child nodes falls below a configurable threshold. This script can be used
e.g. to "fence" the primary following a failover situation where a new primary
has been promoted and all standbys are now child nodes of that primary.
