best practice to migrate server
I'm planning on moving a large active forum to a new server soon. However, the main issue I have is the time it will take for the DNS to update on the domain to the new server. As a result, the only way I can really see to avoid things getting messy with both sites being "active" while the DNS propagates at different times around the world is to disable posting on the old server while things are moving over, and as people get the new DNS info they'll be able to post again as they see the site on the new server.
I understand that setting a low TTL on the domain would pretty much solve this issue, but unfortunately this isn't an option and I'm stuck with the default 24 hours. As far as I'm aware, I'm not able to access the database outside of server itself due to security restrictions, so I can't have both sites pointing at one database either. Or at least I'm not aware of a way of doing it.
I guess the main question I have (and I fear I may know the answer) is if there's any other way to speed up the DNS move or somehow tell the site/domain where to look for the new server? Making the site read-only day or so for a chunk of users obviously isn't ideal, but if it's the only option then I'll have to go that route I guess.