How to fix CoreDNS loop detected in Kubernetes

cat /etc/resolv.conf | head -5

# On systemd-resolved systems, find the real config:
systemctl status systemd-resolved
ls -la /etc/resolv.conf

# Check if it's a symlink (likely on systemd-resolved systems):
cat /run/systemd/resolve/resolv.conf

resolvConf: /run/systemd/resolve/resolv.conf

--resolv-conf=/run/systemd/resolve/resolv.conf

sudo systemctl restart kubelet

# Verify it's running:
sudo systemctl status kubelet

kubectl get pods -n kube-system -l k8s-app=kube-dns
# Or for newer versions:
kubectl get pods -n kube-system -l k8s-app=kube-dns -o wide

kubectl logs -n kube-system -l k8s-app=kube-dns | tail -20

kubectl run -it --rm debug --image=nicolaka/netshoot --restart=Never -- sh

# Inside the pod:
nslookup kubernetes.default
nslookup google.com

# Check kubeadm detected systemd-resolved:
grep resolv /etc/kubernetes/kubelet.conf

# Manually fix all nodes:
sudo kubeadm init phase etcd init
# Restart kubelets on all nodes

# Test internal DNS:
kubectl run test -it --rm --image=alpine -- nslookup kubernetes.default

# Test external DNS:
kubectl run test -it --rm --image=alpine -- nslookup google.com

# Check CoreDNS endpoints:
kubectl get endpoints -n kube-system kube-dns