[Resolved] Kubernetes showing older version of master after successful upgrade

 Issue:- Recently updated my kubernetes cluster

 [root@k8smaster ~]# kubeadm upgrade apply v1.21.3  
 [upgrade/config] Making sure the configuration is correct:  
 [upgrade/config] Reading configuration from the cluster...  
 [addons] Applied essential addon: CoreDNS  
 [addons] Applied essential addon: kube-proxy  
 [upgrade/successful] SUCCESS! Your cluster was upgraded to "v1.21.3". Enjoy!  
 [upgrade/kubelet] Now that your control plane is upgraded, please proceed with upgrading your kubelets if you haven't already done so.  

So the upgrade message clearly shows the cluster was upgraded to "v1.21.3" in master node. However when i run the command to verify

[centos@k8smaster ~]$ kubectl get nodes -o wide
NAME                            STATUS     ROLES                  AGE   VERSION   INTERNAL-IP     EXTERNAL-IP   OS-IMAGE                KERNEL-VERSION                CONTAINER-RUNTIME
k8smaster.unixcloudfusion.in    Ready      control-plane,master   9d    v1.21.2   172.31.36.208   <none>        CentOS Linux 7 (Core)   3.10.0-1160.31.1.el7.x86_64   docker://20.10.7
k8sworker1.unixcloudfusion.in   NotReady   <none>                 9d    v1.21.3   172.31.39.6     <none>        CentOS Linux 7 (Core)   3.10.0-1160.31.1.el7.x86_64   docker://20.10.7
k8sworker2.unixcloudfusion.in   Ready      <none>                 9d    v1.21.3   172.31.46.144   <none>        CentOS Linux 7 (Core)   3.10.0-1160.31.1.el7.x86_64   docker://20.10.7

Even after updating the version still showed v1.21.2

Resolution:-

So the cluster is showing you the old version because you have not updated the kubelet which updates the version in the etcd which is storing all the configuration. So just run the below command to update the kubelet and kubectl

[centos@k8smaster ~]$ sudo yum install -y kubelet kubectl --disableexcludes=kubernetes
Loaded plugins: fastestmirror, versionlock
Loading mirror speeds from cached hostfile
 * base: mirror.centos.org
 * epel: repos.del.extreme-ix.org
 * extras: mirror.centos.org

Updated:
  kubectl.x86_64 0:1.21.3-0

Updated:
  kubelet.x86_64 0:1.21.3-0

Complete!

Once the update is complete for both the kubectl and kubelet , now verify the version again

[centos@k8smaster ~]$ kubectl get nodes -o wide
NAME                            STATUS     ROLES                  AGE   VERSION   INTERNAL-IP     EXTERNAL-IP   OS-IMAGE                KERNEL-VERSION                CONTAINER-RUNTIME
k8smaster.unixcloudfusion.in    Ready      control-plane,master   9d    v1.21.3   172.31.36.208   <none>        CentOS Linux 7 (Core)   3.10.0-1160.31.1.el7.x86_64   docker://20.10.7
k8sworker1.unixcloudfusion.in   NotReady   <none>                 9d    v1.21.3   172.31.39.6     <none>        CentOS Linux 7 (Core)   3.10.0-1160.31.1.el7.x86_64   docker://20.10.7
k8sworker2.unixcloudfusion.in   Ready      <none>                 9d    v1.21.3   172.31.46.144   <none>        CentOS Linux 7 (Core)   3.10.0-1160.31.1.el7.x86_64   docker://20.10.7

So the issue is resolved and it shows the new version