How to customize rke2-coredns

The name and namespace should match the ones used when deploying the package using HelmChart. The valuesContent section contains the values that you want to customize, and they will be processed like when being passed to helm directly.
For our case, we will add a new zone to coreDNS using the zoneFiles directive. You can download the coreDNS package to review the values.yml to find out the directives available for customization [2]. Or you can look at the values.yml available from the rke2-coredns charts for your version [3].

A file /var/lib/rancher/rke2/server/manifests/rke2-coredns-config.yaml should be created with similar content. After that, the rke2-server service should be restarted to apply the change. 

apiVersion: helm.cattle.io/v1
kind: HelmChartConfig
metadata:
  name: rke2-coredns
  namespace: kube-system
spec:
  valuesContent: |-
    zoneFiles:
      - filename: doit.tech.conf
        domain: doit.tech
        contents: |
          doit.tech:53 {
              errors
              cache 30
              forward . 10.0.254.1
          }

The configmap rke2-coredns-rke2-coredns can be reviewed to determine if the change was successful.

kubectl -n kube-system get configmap rke2-coredns-rke2-coredns -o json