My kubernetes cluster IP address changed and now kubectl will no longer connect - kubernetes

Question

Running under Ubuntu I used kubeadm init to setup my cluster (master node) and copied over the /etc/kubernetes/admin.conf $HOME/.kube/config and all was well when using kubectl.
However after a reboot my master node has had an IP address change which is not the same as what is in $HOME/.kube/config so now I can no longer connect kubectl
So how do I regenerate the admin.conf now that I have a new IP address? Running kubeadm init will just kill everything which is not what I want.

Answer 1

I found this solution on the internet and it works for me:
systemctl stop kubelet docker
cd /etc/
mv kubernetes kubernetes-backup
mv /var/lib/kubelet /var/lib/kubelet-backup
mkdir -p kubernetes
cp -r kubernetes-backup/pki kubernetes
rm kubernetes/pki/{apiserver.*,etcd/peer.*}
systemctl start docker
kubeadm init --ignore-preflight-errors=DirAvailable--var-lib-etcd
#Run "kubeadm reset" on all nodes if was this error "error execution phase preflight: [preflight] Some fatal errors occurred:
[ERROR FileAvailable--etc-kubernetes-kubelet.conf]: /etc/kubernetes/kubelet.conf already exists
[ERROR Port-10250]: Port 10250 is in use
[ERROR FileAvailable--etc-kubernetes-pki-ca.crt]: /etc/kubernetes/pki/ca.crt already exists"
cp kubernetes/admin.conf ~/.kube/config
kubectl get nodes --sort-by=.metadata.creationTimestamp
kubectl delete node $(kubectl get nodes -o jsonpath='{.items[(#.status.conditions[0].status=="Unknown")].metadata.name}')
kubectl get pods --all-namespaces
After These, Join your Slaves to Master.
Reference: https://medium.com/#juniarto.samsudin/ip-address-changes-in-kubernetes-master-node-11527b867e88

Answer 2

The following command can be used to regenerate admin.conf
kubeadm alpha phase kubeconfig admin --apiserver-advertise-address <new_ip>
However, if you use an IP instead of a hostname, your API-server certificate will be invalid. So, either regenerate your certs ( kubeadm alpha phase certs renew apiserver ), use hostnames instead of IPs or add the insecure --insecure-skip-tls-verify flag when using kubectl

Answer 3

You do not want to use kubeadm reset. That will reset everything and you would have to start configuring your cluster again.
Well, in your scenario, please have a look on the steps below:
nano /etc/hosts (update your new IP against YOUR_HOSTNAME)
nano /etc/kubernetes/config (configuration settings related to your cluster) here in this file look for the following params and update accordingly
KUBE_MASTER="--master=http://YOUR_HOSTNAME:8080"
KUBE_ETCD_SERVERS="--etcd-servers=http://YOUR_HOSTNAME:2379" #2379 is default port
nano /etc/etcd/etcd.conf (conf related to etcd)
KUBE_ETCD_SERVERS="--etcd-servers=http://YOUR_HOSTNAME/WHERE_EVER_ETCD_HOSTED:2379"
2379 is default port for etcd. and you can have multiple etcd servers defined here comma separated
Restart kubelet, apiserver, etcd services.
It is good to use hostname instead of IP to avoid such scenarios.
Hope it helps!