Comment by scott_w

A story from 10 years ago providing services to the education sector:

I did exactly what you suggested, even leaving extra time (a full weekend!) for the DNS changes to propagate. What happened?

Turns out local authorities don't all respect DNS TTL settings and we had a major outage. I had to on-the-fly learn how to configure iptables to act as a proxy for the new server.

The "proxy" was still receiving requests 2 weeks later.