I'm trying to add a custom domain to my AKS cluster. All of the components I'm dealing with are within the same VNET, but the custom DNS Server and AKS Service are in different subnets. I've also like to avoid changing the DNS Server at the VNET level.

I've followed this guide to no avail:

https://docs.microsoft.com/en-us/azure/aks/coredns-custom#use-custom-domains

I've also found previous answers used a similar setup:

Resolve custom dns in kubernetes cluster (AKS)

but that did not work either. The difference between the two being the coredns plugin that is used to forward the resolving traffic towards a custom resolver.

I've tried both the proxy and forward plugin with the same setup, and both end in the same error

Proxy plugin:

apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns-custom
  namespace: kube-system
data:
  test.server: |
    mydomain.com:53 {
        log
        errors
        proxy . [MY DNS SERVER'S IP]
    }

Forward Plugin:

apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns-custom
  namespace: kube-system
data:
  test.server: |
     mydomain.com:53 {
        log
        errors
        forward . [MY DNS SERVER'S IP]
    }

Reproduce:

1 VNET

2 Subnets (1 for AKS, 1 for the DNS VM)

Add a name to the DNS VM, and use a configmap to proxy traffic to the custom DNS instead of the node resolvers/VNET DNS

Error:

After applying either of the configmaps above, the coredns pods log this error:

2019-11-11T18:41:46.224Z [INFO] 172.28.18.104:47434 - 45605 "A IN mydomain.com. udp 55 false 512" REFUSED qr,rd 55 0.001407305s