Users report that pods in your cluster cannot resolve service names, though pod-to-pod IP connectivity works. You run 'kubectl get pods -n kube-system' and see that both CoreDNS pods are stuck in 'Pending' status. Describing one pod shows the event: '0/3 nodes are available: 3 node(s) had untolerated taint {node.kubernetes.io/not-ready: }'. What is the most likely root cause you should investigate first?