That is a DNS response, meaning that you have that FQDN pointing to one controller. If we look at AP’s being on the same subnet as multiple controllers for example... There is information sent to the ap that includes number of joined access points. AP will choose what controller it will join depending on the traffic formation that is presented to the requested joining ap. The ap will make a decision.
You can search this on the internet for additional references: cisco capwap ap join process
-Scott
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