The named DNS server includes the ability to send notify messages to other master and slave servers (https://www.zytrax.com/books/dns/ch7/xfer.html#notify https

The named DNS server includes the ability to send notify messages to other master and slave servers (https://www.zytrax.com/books/dns/ch7/xfer.html#notify https://www.zytrax.com/books/dns/ch7/xfer.html#notify) when changes are made to records. Perhaps Route 53 and Google have setup a system to notify each other when a record changes so they can then request a transfer and have near zero propagation delay. Note that this notify system is not the same as that proposed in the RFC. This notify system is configured by the admin and is meant to keep secondary servers updated with changes in the primary server, not for general notification of changes to anyone who is interested.