Inklings: a tumblelog

The nsnotifyd daemon monitors a set of DNS zones and runs a command when any of them change. It listens for DNS NOTIFY messages so it can respond to changes promptly. It also uses each zone’s SOA refresh and retry parameters to poll for updates if nsnotifyd does not receive NOTIFY messages more frequently.

Anywhere you currently have a cron job which is monitoring updates to DNS zones, you might want to run it under nsnotifyd instead of cron, so your script runs as soon as the zone changes instead of running at fixed intervals.