Custom router/monitor module?

[John Yuhos]

Is it possible to run my own external or custom monitor module/script? Currently, we use proxysql + a home-grown script to detect master failures, replication lag, etc.  This script runs every 5 seconds and sets the master, slave, down status in proxysql, it will also email/slack message the admin team.  Our setup is unique, we have a master master setup. However, our application requires a single primary master, with a secondary master only for emergency failover/backup.  We cannot split read or writes to our secondary master due to replication lag causing application failures.  Any tips would be greatly appreciated.