My core dns corefile got corrupted somehow and now I need to regenerate it or reset it to it's default installed value. How do I do that? I've tried copying and pasting a locally-saved version of the file via kubectl edit cm coredns -n kube-system but I get validation errors
error: configmaps "coredns" is invalid
A copy of your changes has been stored to "/tmp/kubectl-edit-suzaq.yaml"
error: Edit cancelled, no valid changes were saved.When you directly edit the setting, it used to give the error.
What can you do?
before you run anything, please take a backup:
kubectl -n kube-system get configmap coredns -o yaml > coredns.yamlkubectl apply --force -f /tmp/kubectl-edit-suzaq.yamlIn most cases, it will apply the latest setting successfully by this way. If failed, go through the error, update the file /tmp/kubectl-edit-suzaq.yaml and forcely apply again.
kubectl -n kube-system get configmap coredns -o yaml > coredns.yaml
# do a backup, if you don't 100% sure the change will work
cp coredns.yaml coredns.yaml.orig
# update the change in coredns.yaml
# delete coredns
kubectl delete configmap coredns
# apply new change
kubectl apply -f coredns.yamlBe careful, above steps will generate outage. if you work on a prod environment, you should think about to backup all kubernetes setting before doing above change.