New cluster config doc

Author: laurenhughes

articles/aks/TOC.yml

@@ -126,6 +126,8 @@
       href: upgrade-cluster.md
     - name: Process node OS updates
       href: node-updates-kured.md
+    - name: Configure an AKS cluster
+      href: configure-cluster.md
     - name: Delete an AKS cluster
       href: /cli/azure/aks#az-aks-delete
       maintainContext: true

articles/aks/cluster-configuration.md

@@ -0,0 +1,78 @@
+---
+title: Cluster configuration in Azure Kubernetes Services (AKS)
+description: Learn how to configure a cluster in Azure Kubernetes Service (AKS)
+services: container-service
+ms.topic: conceptual
+ms.date: 03/12/2020
+---
+
+# Configure an AKS cluster
+
+As part of creating an AKS cluster, you may need to customize your cluster configuration to suit your needs. This article introduces a few options for customizing your AKS cluster.
+
+## OS configuration (Preview)
+
+AKS now supports Ubuntu 18.04 as the node operating system (OS) in preview. During the preview period, both Ubuntu 16.04 and Ubuntu 18.04 are available. To continue using clusters with Ubuntu 16.04, do not add the `--aks-custom-headers` tag as shown in the following examples.
+
+You must have the following resources installed:
+
+- The Azure CLI, version 2.2.0 or later
+- The aks-preview 0.4.35 extension
+
+To install the aks-preview 0.4.35 extension or later, use the following Azure CLI commands:
+
+```azurecli
+az extension add --name aks-preview
+az extension list
+```
+
+> [!CAUTION]
+> After you register a feature on a subscription, you can't currently unregister that feature. When you enable some preview features, defaults might be used for all AKS clusters created afterward in the subscription. Don't enable preview features on production subscriptions. Instead, use a separate subscription to test preview features and gather feedback.
+
+```azurecli
+az feature register --name UseCustomizedUbuntuPreview --namespace Microsoft.ContainerService
+```
+
+It might take several minutes for the status to show as **Registered**. You can check the registration status by using the [az feature list](https://docs.microsoft.com/cli/azure/feature?view=azure-cli-latest#az-feature-list) command:
+
+```azurecli
+az feature list -o table --query "[?contains(name, 'Microsoft.ContainerService/UseCustomizedUbuntuPreview')].{Name:name,State:properties.state}"
+```
+
+When the status shows as registered, refresh the registration of the `Microsoft.ContainerService` resource provider by using the [az provider register](https://docs.microsoft.com/cli/azure/provider?view=azure-cli-latest#az-provider-register) command:
+
+```azurecli
+az provider register --namespace Microsoft.ContainerService
+```
+
+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
+az aks create --name myAKSCluster --resource-group myResourceGroup --aks-custom-headers CustomizedUbuntu=aks-ubuntu-1804
+```
+
+## 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.
+
+To specify your own resource group name, install the aks-preview Azure CLI extension version 0.3.2 or later. Using the Azure CLI, use the `--node-resource-group` parameter of the `az aks create` command to specify a custom name for the resource group. If you use an Azure Resource Manager template to deploy an AKS cluster, you can define the resource group name by using the `nodeResourceGroup` property.
+
+```azurecli
+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. 
+
+As you work with the node resource group, keep in mind that you cannot:
+
+- Specify an existing resource group for the node resource group.
+- Specify a different subscription for the node resource group.
+- Change the node resource group name after the cluster has been created.
+- Specify names for the managed resources within the node resource group.
+- Modify or delete Azure-created tags of managed resources within the node resource group.
+
+## Next steps
+
+- Learn how to use Kured to [apply security and kernel updates to Linux nodes](node-updates-kured.md) in your cluster.
+- See [Upgrade an Azure Kubernetes Service (AKS) cluster](upgrade-cluster.md) to learn how to upgrade your cluster to the latest version of Kubernetes.
+- See the list of [Frequently asked questions about AKS](faq.md) to find answers to some common AKS questions.