Update nodelocaldns.md with config steps. (#18716)

Remove references to 169.254.20.10 as the default.

Update content/en/docs/tasks/administer-cluster/nodelocaldns.md
Co-Authored-By: Tim Bannister <[email protected]>

Author: prameshj

content/en/docs/tasks/administer-cluster/nodelocaldns.md

@@ -2,6 +2,7 @@
 reviewers:
 - bowei
 - zihongz
+- sftim
 title: Using NodeLocal DNSCache in Kubernetes clusters
 content_template: templates/task
 ---
@@ -47,18 +48,44 @@ This is the path followed by DNS Queries after NodeLocal DNSCache is enabled:
 {{< figure src="/images/docs/nodelocaldns.jpg" alt="NodeLocal DNSCache flow" title="Nodelocal DNSCache flow" caption="This image shows how NodeLocal DNSCache handles DNS queries." >}}
 
 ## Configuration
-
-This feature can be enabled using the command:
-
-`KUBE_ENABLE_NODELOCAL_DNS=true kubetest --up`
-
-This works for e2e clusters created on GCE. On all other environments, the following steps will setup NodeLocal DNSCache:
-
-* A yaml similar to [this](https://github.com/kubernetes/kubernetes/blob/master/cluster/addons/dns/nodelocaldns/nodelocaldns.yaml) can be applied using `kubectl create -f` command.
-* No need to modify the --cluster-dns flag since NodeLocal DNSCache listens on both the kube-dns service IP as well as a link-local IP (169.254.20.10 by default)
+{{< note >}} The local listen IP address for NodeLocal DNSCache can be any IP in the 169.254.20.0/16 space or any other IP address that can be guaranteed to not collide with any existing IP. This document uses 169.254.20.10 as an example.
+{{< /note >}}
+
+This feature can be enabled using the following steps:
+
+* Prepare a manifest similar to the sample [`nodelocaldns.yaml`](https://github.com/kubernetes/kubernetes/blob/master/cluster/addons/dns/nodelocaldns/nodelocaldns.yaml) and save it as `nodelocaldns.yaml.`
+* Substitute the variables in the manifest with the right values: 
+
+     * kubedns=`kubectl get svc kube-dns -n kube-system -o jsonpath={.spec.clusterIP}` 
+   
+     * domain=`<cluster-domain>` 
+   
+     * localdns=`<node-local-address>`
+  
+     `<cluster-domain>` is "cluster.local" by default. `<node-local-address>` is the local listen IP address chosen for NodeLocal DNSCache.
+
+   * If kube-proxy is running in IPTABLES mode: 
+   
+     ``` bash
+     sed -i "s/__PILLAR__LOCAL__DNS__/$localdns/g; s/__PILLAR__DNS__DOMAIN__/$domain/g; s/__PILLAR__DNS__SERVER__/$kubedns/g" nodelocaldns.yaml
+     ```
+     
+     `__PILLAR__CLUSTER__DNS__` and `__PILLAR__UPSTREAM__SERVERS__` will be populated by the node-local-dns pods.  
+     In this mode, node-local-dns pods listen on both the kube-dns service IP as well as `<node-local-address>`, so pods can lookup DNS records using either IP address.
+
+  * If kube-proxy is running in IPVS mode: 
+  
+    ``` bash
+     sed -i "s/__PILLAR__LOCAL__DNS__/$localdns/g; s/__PILLAR__DNS__DOMAIN__/$domain/g; s/__PILLAR__DNS__SERVER__//g; s/__PILLAR__CLUSTER__DNS__/$kubedns/g" nodelocaldns.yaml
+    ```
+     In this mode, node-local-dns pods listen only on `<node-local-address>`. The node-local-dns interface cannot bind the kube-dns cluster IP since the interface used for IPVS loadbalancing already uses this address.  
+     `__PILLAR__UPSTREAM__SERVERS__` will be populated by the node-local-dns pods.
+  
+* Run `kubectl create -f nodelocaldns.yaml`
+* If using kube-proxy in IPVS mode, `--cluster-dns` flag to kubelet needs to be modified to use `<node-local-address>` that NodeLocal DNSCache is listening on.
+  Otherwise, there is no need to modify the value of the `--cluster-dns` flag, since NodeLocal DNSCache listens on both the kube-dns service IP as well as `<node-local-address>`.
 
 Once enabled, node-local-dns Pods will run in the kube-system namespace on each of the cluster nodes. This Pod runs [CoreDNS](https://github.com/coredns/coredns) in cache mode, so all CoreDNS metrics exposed by the different plugins will be available on a per-node basis.
 
-The feature can be disabled by removing the daemonset, using `kubectl delete -f` command. On e2e clusters created on GCE, the daemonset can be removed by deleting the node-local-dns yaml from `/etc/kubernetes/addons/0-dns/nodelocaldns.yaml`
-
+You can disable this feature by removing the DaemonSet, using `kubectl delete -f <manifest>` . You should also revert any changes you made to the kubelet configuration.
  {{% /capture %}}