How "last" works in dns_order

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.


@Tieske might be able to help out here.

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.


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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.