Is it possible to change CIDR network flannel on running Kubernetes cluster? If yes what will happen with the launched pods?



I've managed to change Flannel CIDR network pool in the following way:

Assuming that you have installed a fresh k8s cluster via kubeadm builder tool with adopting appropriate --pod-network-cidr flag in kubeadm init command:

Override podCIDR parameter on the particular k8s Node resource with a new IP source range, desirable way with piping output:

$ kubectl get no $hostname -o yaml >> file.yaml | sed -i "s~$old_ip~$new_ip~" file.yaml| kubectl delete no $hostname && kubectl create -f file.yaml

Replace "Network" field under net-conf.json header in the relevant Flannel ConfigMap with a new network IP range:

$ kubectl edit cm kube-flannel-cfg -n kube-system

net-conf.json: | { "Network": "", "Backend": { "Type": "vxlan" } }

Wipe current CNI network interfaces remaining the old network pool:

$ sudo ip link del cni0; sudo ip link del flannel.1

Re-spawn Flannel and CoreDNS pods respectively:

$ kubectl delete pod --selector=app=flannel -n kube-system
$ kubectl delete pod --selector=k8s-app=kube-dns -n kube-system

Wait until CoreDNS pods obtain IP address from a new network pool. Keep in mind that your custom Pods will still retain the old IP addresses inside containers unless you re-create them manually as well.

  • Why is it so involved? I just went and used kubeadm reset and started building the cluster from scratch with another setting for --pod-network-cidr. It would make sense if kubeadm would provide simple cli support to change this setting. Oct 26 '21 at 11:38

For calico, create new IPpool and and disable old.... https://projectcalico.docs.tigera.io/networking/migrate-pools

New contributor
Vivek Shinde is a new contributor to this site. Take care in asking for clarification, commenting, and answering. Check out our Code of Conduct.
  • While this link may answer the question, it is better to include the essential parts of the answer here and provide the link for reference. Link-only answers can become invalid if the linked page changes. - From Review
    – Dave M
    2 days ago

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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