Merge pull request #115470 from palma21/aks-naming-rules

Update aks-naming-rules and 1804 nodepool create

Author: Court72

articles/aks/cluster-configuration.md

@@ -44,6 +44,8 @@ When the status shows as registered, refresh the registration of the `Microsoft.
 az provider register --namespace Microsoft.ContainerService
 ```
 
+### New clusters
+
 Configure the cluster to use Ubuntu 18.04 when the cluster is created. Use the `--aks-custom-headers` flag to set the Ubuntu 18.04 as the default OS.
 
 ```azure-cli
@@ -52,6 +54,17 @@ az aks create --name myAKSCluster --resource-group myResourceGroup --aks-custom-
 
 If you want to create a regular Ubuntu 16.04 cluster, you can do so by omitting the custom `--aks-custom-headers` tag.
 
+### Existing clusters
+
+Configure a new node pool to use Ubuntu 18.04. Use the `--aks-custom-headers` flag to set the Ubuntu 18.04 as the default OS for that node pool.
+
+```azure-cli
+az aks nodepool add --name ubuntu1804 --cluster-name myAKSCluster --resource-group myResourceGroup --aks-custom-headers CustomizedUbuntu=aks-ubuntu-1804
+```
+
+If you want to create a regular Ubuntu 16.04 node pools, you can do so by omitting the custom `--aks-custom-headers` tag.
+
+
 ## Custom resource group name
 
 When you deploy an Azure Kubernetes Service cluster in Azure, a second resource group gets created for the worker nodes. By default, AKS will name the node resource group `MC_resourcegroupname_clustername_location`, but you can also provide your own name.
@@ -62,9 +75,9 @@ To specify your own resource group name, install the aks-preview Azure CLI exten
 az aks create --name myAKSCluster --resource-group myResourceGroup --node-resource-group myNodeResourceGroup
 ```
 
-The secondary resource group is automatically created by the Azure resource provider in your own subscription. Note that you can only specify the custom resource group name when the cluster is created. 
+The secondary resource group is automatically created by the Azure resource provider in your own subscription. You can only specify the custom resource group name when the cluster is created. 
 
-As you work with the node resource group, keep in mind that you cannot:
+As you work with the node resource group, keep in mind that you can't:
 
 - Specify an existing resource group for the node resource group.
 - Specify a different subscription for the node resource group.

articles/aks/kubernetes-walkthrough-portal.md

@@ -45,7 +45,7 @@ To create an AKS cluster, complete the following steps:
 
 4. On the **Scale** page, keep the default options. At the bottom of the screen, click **Next: Authentication**.
     > [!CAUTION]
-    > Creating new AAD Service Principals may take multiple minutes to propagate and become available causing Service Principal not found errors and validation failures in Azure portal. If you hit this please visit [here](troubleshooting.md#im-receiving-errors-that-my-service-principal-was-not-found-when-i-try-to-create-a-new-cluster-without-passing-in-an-existing-one) for mitigations.
+    > Creating new AAD Service Principals may take multiple minutes to propagate and become available causing Service Principal not found errors and validation failures in Azure portal. If you hit this please visit [here](troubleshooting.md#received-an-error-saying-my-service-principal-wasnt-found-or-is-invalid-when-i-try-to-create-a-new-cluster) for mitigation.
 
 5. On the **Authentication** page, configure the following options:
     - Create a new service principal by leaving the **Service Principal** field with **(new) default service principal**. Or you can choose *Configure service principal* to use an existing one. If you use an existing one, you will need to provide the SPN client ID and secret.