It depends on how you set dns up, I'm looking at the docs for Advanced Server Installation > DNS. If your CoreDNS is setup as a clusterIP it will only be reachable internally, and getting to it from the outside via ingress might be a little squirrely. What you really need to do is have coredns running somewhere where it's bound to the node IP + clusterIP. That way it's running in the same place, just with an outside and inside interface.... and I'm honestly not even familiar enough with kubernetes to know whether or not that's possible