CoreDNS is the default DNS addon in Kubernetes since 1.13. I recently needed to switch back to kube-dns for some testing, and it wasn’t obvious from the documentation how to do that. Here’s how I went about it for reference.

These steps assume kubeadm 1.13.

Steps

First, initialise the master node, skipping the coredns addon phase:

kubeadm init --pod-network-cidr=10.244.0.0/16 --skip-phases=addon/coredns

Then prepare a kubeadm override config to specify kube-dns is to be used instead of the default:

$ cat > kubeadm-kube-dns.yaml << EOF
apiVersion: kubeadm.k8s.io/v1beta1
kind: ClusterConfiguration
dns:
    type: "kube-dns"
    imageRepository: myregistry:5000
EOF

This example also shows how to use a custom repository for the images.

Now init the addon:

kubeadm init phase addon coredns --config=kubeadm-kube-dns.yaml

Finally, add your CNI addon of choice to finish setting up the master:

kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml

That’s it. I also found the following steps from IBM useful to verify the DNS is sane (remember to add a k8s worker before proceeding with this):

kubectl create -f https://k8s.io/examples/admin/dns/busybox.yaml
kubectl exec -ti busybox -- nslookup kubernetes.default