I have a dns server running at for custom domains like .fritz.box. Having a single node cluster on k3s, Rancher was installed using a subdomain server2.fritz.box using this command:

    helm install rancher-latest/rancher \
      --name rancher \
      --namespace cattle-system \
      --set hostname=server2.fritz.box

Rancher itself shows that some services are not avaliable and the logs from cattle say server2.fritz.box is not avaliable. Since Kubernetes has its own dns system, I looked at the documentation and it seems that I need to set my .19 dns server so that Kubernetes knows how to resolve .fritz.box domains. Some questions also have similar problems like https://stackoverflow.com/questions/41448095/kube-dns-does-not-resolve-external-hosts-on-kubeadm-bare-metal-cluster

So I created the following yaml:

# https://github.com/kubernetes/kops/issues/4986
apiVersion: v1
kind: ConfigMap
  name: kube-dns
  namespace: kube-system
  stubDomains: |
    {"fritz.box": [""]}
  upstreamNameservers: |

Loaded with kubectl apply -f dns.yml. Now created a busybox test pod:

~$ kubectl exec -it busybox -- ping server2.fritz.box
ping: bad address 'server2.fritz.box'

Why is this not working? And what must be done to resolve a custom dns server in Kubernetes?

2 Answers 2


ibuildthecloud9 gave me the right hint. Since the github issue doesn't describe how to midify the dns, I figured it out and want to document it here in case someone need to change it, too. It's stored in the configmap coredns as Corefile:

proxy .

You need to replace this by your dns server ( in my case). It could be done manually using kubectl edit cm -n kube-system coredns. In case you also want to automate this process:

kubectl get cm -n kube-system coredns -o yaml | sed "s/proxy . ." > coredns-fixed.yml

Now you'll have the fixed yaml file, which got loaded by

kubectl apply -f coredns-fixed.yml

Test it

Create busybox.yml

apiVersion: v1
kind: Pod
    name: busybox
    # for arm
    #- image: hypriot/armhf-busybox
    - image: busybox
          - sleep
          - "3600"
      imagePullPolicy: IfNotPresent
      name: busybox
    restartPolicy: Always

Create the pod: kubectl create -f busybox.yml And try to ping a host resolved by your dns:

~$ kubectl exec -it busybox -- ping -c1 server2.fritz.box
PING server2.fritz.box ( 56 data bytes
64 bytes from seq=0 ttl=61 time=0.386 ms

Before applying our dns (so was used, which belongs to Cloudflare) this throws the following resolving error:

*~$ kubectl exec -it busybox -- ping -c1 server2.fritz.box
ping: bad address 'server2.fritz.box'*

I believe this is an current bug in k3s that upstream DNS is hardcoded to this should be resolved shortly https://github.com/rancher/k3s/issues/53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.