kubeadm-reset: add notes about more manual cleanup steps

Author: neolit123

content/en/docs/reference/setup-tools/kubeadm/kubeadm-reset.md

@@ -22,7 +22,10 @@ etcd member of this node from the etcd cluster.
 To skip a list of phases you can use the `--skip-phases` flag, which works in a similar way to
 the `kubeadm join` and `kubeadm init` phase runners.
 
-### External etcd clean up
+`kubeadm reset` also supports the `--config` flag for passing
+a [`ResetConfiguration` structure](/docs/reference/config-api/kubeadm-config.v1beta4/).
+
+### Cleanup of external etcd members
 
 `kubeadm reset` will not delete any etcd data if external etcd is used. This means that if you run `kubeadm init` again using the same etcd endpoints, you will see state from previous clusters.
 
@@ -34,6 +37,64 @@ etcdctl del "" --prefix
 
 See the [etcd documentation](https://github.com/coreos/etcd/tree/master/etcdctl) for more information.
 
+### Cleanup of CNI configuration
+
+CNI plugins use the directory `/etc/cni/net.d` to store their configuration.
+The `kubeadm reset` command does not cleanup that directory. Leaving the configuration
+of a CNI plugin on a host can be problematic if the same host is later used
+as a new Kubernetes node and a different CNI plugin happens to be deployed in that cluster.
+It can result in a configuration conflict between CNI plugins.
+
+To cleanup the directory, backup its contents if needed and then execute
+the following command:
+
+```bash
+sudo rm -rf /etc/cni/net.d
+```
+
+### Cleanup of network traffic rules
+
+The `kubeadm reset` command does not clean any iptables, nftables or IPVS rules applied
+to the host by kube-proxy. A control loop in kube-proxy ensures that the rules on each node
+host are synchronized. For additional details please see
+[Virtual IPs and Service Proxies](/docs/reference/networking/virtual-ips/).
+
+Leaving the rules without cleanup should not cause any issues if the host is
+later reused as a Kubernetes node or if it will serve a different purpose.
+
+If you wish to perform this cleanup, you can use the same kube-proxy container
+which was used in your cluster and the `--cleanup` flag of the
+`kube-proxy` binary:
+
+```bash
+docker run --privileged --rm registry.k8s.io/kube-proxy:v{{< skew currentPatchVersion >}} sh -c "kube-proxy --cleanup && echo DONE"
+```
+
+The output of the above command should print `DONE` at the end.
+Instead of Docker, you can use your preferred container runtime to start the container.
+
+### Cleanup of $HOME/.kube
+
+The `$HOME/.kube` directory typically contains configuration files and kubectl cache.
+While not cleaning the contents of `$HOME/.kube/cache` is not an issue, there is one important
+file in the directory. That is `$HOME/.kube/config` and it is used by kubectl to authenticate
+to the Kubernetes API server. After `kubeadm init` finishes, the user is instructed to copy the
+`/etc/kubernetes/admin.conf` file to the `$HOME/.kube/config` location and grant the current
+user access to it.
+
+The `kubeadm reset` command does not clean any of the contents of the `$HOME/.kube` directory.
+Leaving the `$HOME/.kube/config` file without deleting it, can be problematic depending
+on who will have access to this host after `kubeadm reset` was called.
+If the same cluster continues to exist, it is highly recommended to delete the file,
+as the admin credentials stored in it will continue to be valid.
+
+To cleanup the directory, examine its contents, perform backup if needed and execute
+the following command:
+
+```bash
+rm -rf $HOME/.kube
+```
+
 ### Graceful kube-apiserver shutdown
 
 If you have your `kube-apiserver` configured with the `--shutdown-delay-duration` flag,