This is one of the cases where the passive check of the Nagios monitoring system comes in handy as we need to be informed immediately when the Keepalived changes state. So you will need an NSCA system implemented with your Nagios configuration.
Studying the Keepalived configuration we found that the authors have implemented the option to run a script that when the state of the VRRP changes. The script I’m referring to is run under the “notify” option.