> The model I've been trying recently is to make DNS changes in three parts. First: change existing DNS entry TTL from 1hr to 1s. Wait 1hr as the caches clear.

> The model I've been trying recently is to make DNS changes in three parts. First: change existing DNS entry TTL from 1hr to 1s. Wait 1hr as the caches clear. Update entry to the new address, keeping 1s TTL. Wait, test, and monitor for a while. Finally, increase the TTL back to 1hr. It takes more planning, but I avoid a 1hr partial outage if I mess up the address. This is my preferred way of doing it, especially for MX records.