Override CoreDNS config to forward server

If what AI suggested doesn't work

You might think that you can configure CoreDNS to forward requests for some specific domain to some other DNS server, like this:

apiVersion: v1
kind: ConfigMap
metadata:
  name: coredns-custom
  namespace: kube-system
data:
  test1.override: |
    forward example.com 1.1.1.1

But unfortunately, this won't work, because of the way how these *.overrides work. They are included at the end of CoreDNS's main config file. Unfortunately, in k3s, this file first says forward . /etc/resolv.conf - i.e. forward everything... and since forward statements are processed in the order they are listed, your forward statement is effectively ignored.

The way how you do it is:

1. First, look at the existing CoreDNS config file (it starts with .:53 { and ends with }\nimport /etc/coredns/custom/*.server)

2. Then, you write a new server block, like this (and add it to the data: part of your coredns-custom ConfigMap):

    test2.server: |
      example.com:53 {
        forward . 1.1.1.1
      }
   

This means that you now create a new server, and all requests are forwarded to the mentioned DNS server. Nice!

Source: it was mentioned in this github issue.