[IgorPartola]

I think the more likely explanation is the behavior I have seen in IE8 and below where DNS entries get cached and as long as the server responds correctly, they cache is not busted. On one particular upgrade we brought the TTL down to 60 seconds and had to wait three days for the traffic to subside.

Also, at least older versions of nginx in reverse proxying mode have the same issue. Had to send the nginx processes a SIGHUP or restart them entirely, don't remember which, to get them to use the new IP's.

[Dylan16807]

I recently learned the hard way that Firefox has a cache that does the same thing. Obsolete documentation lists a 60 second cache but I watched it making requests to the wrong server almost an entire day after the (3 hour TTL) records were changed. And yes, I checked that other apps showed the right IP.

https://bugzilla.mozilla.org/show_bug.cgi?id=861273

https://bugzilla.mozilla.org/show_bug.cgi?id=709976

[ceejayoz]

I believe some ISPs have a TTL threshold under which they use their internal default. i.e. a TTL of 60 seconds would be ignored and become 86400, whereas a 3600 second TTL might still be respected.