I am reviewing my DNS configuration, and was hoping to get clarification around the role that “last” plays in DNS resolution (dns_order). Does anybody know of documentation around that configuration beyond the comments included with it? I am exploring some issues where certain upstreams aren’t properly switching when their A name changes. I just want to make sure i understand how it functions.
Thanks.
Default is: last, srv, a, cname.
“Last” is a small optimization (last successful lookup type), say a name resolves to an A record, the first time it will try an srv, if that fails it will try an A, which then succeeds.
When the record expires, and is being renewed, since we have a previous success, it will first try “last”, which in this case is the A. Without first trying the Srv one.
The full order would be A (last), srv, (A here is now skipped because it was tried already as “last”) and then cname.
So it might only have an impact of your record type changed.
Hth
Thank you. That was my guess, but I wanted to make sure. I also see no reason it would be related to the issue I am exploring.