how can I change CNI in Kubernetes ?

To change the CNI (Container Network Interface) in a Kubernetes cluster, you will need to follow these steps in detail:

1. Identify the current CNI in use by checking the kubelet configuration on each node. You can do this by looking at the --network-plugin flag or by checking the cni0 interface in the /etc/cni directory.
2. Drain and cordon the node to prevent new pods from being scheduled on it. This can be done using the command kubectl drain <node-name> --ignore-daemonsets
3. Uninstall the current CNI and any associated plugins. You can use the CNI's specific installation instructions to uninstall it.
4. Install the new CNI and any associated plugins. You can use the CNI's specific installation instructions to install it.
5. Update the kubelet configuration to use the new CNI. You can do this by updating the --network-plugin flag in the kubelet configuration file or by updating the cni0 interface in the /etc/cni directory.
6. Uncordon the node to allow new pods to be scheduled on it. This can be done using the command kubectl uncordon <node-name>

It is important to test the new CNI in a non-production environment before applying the changes to a production cluster. It is also good to have a backup plan in case of unexpected issues or errors.

It is also important to note that changing the CNI can have a significant impact on the existing pods and services running in the cluster. So, it is important to perform this change during a maintenance window or during a non-critical time.