I did read a bunch of relevant Q/A here but I am still not sure what the best answer is.
I'm moving a couple of sites from IP address "1.a.b.c" to "2.d.e.f". As of right now in the existing DNS I set all TTL to 300 seconds, and I have a new DNS zone ready to be used (on AWS Route 53), with new nameservers and all TTLs at 60 seconds. So I believe I am ready, from a DNS perspective. Post-move, after a few days I will set TTL to more reasonable numbers at Route 53.
I've warned all my users about the move and I have a defined window of time for the move. I told them that once the move is complete and if 24 hours have gone by and they still see the old (locked) sites, they should reboot their computer to force a local DNS cache flush.
I do not understand how the user's browser (cache) plays a role in this. My own experiments with a local hosts file (Win7) tell me there is something about the browser that is not letting the old IP address go -- I had to go to history->clear everything in order to get the new site location to show up, even after
(EDIT) - I do not have root access to the old server, so I can't implement the accepted answer to this question.
Question: I really don't want my users to have to deal with that, so is there something I can do to force all the browsers out there to re-cache? And if so, how long do I leave it turned on?