Update reliability-hdinsight-on-aks.md in az support section

Author: fengzhou-msft

articles/reliability/reliability-hdinsight-on-aks.md

@@ -32,7 +32,39 @@ This article describes reliability support in [Azure HDInsight on Azure Kubernet
 
 [!INCLUDE [next step](includes/reliability-availability-zone-description-include.md)]
 
-Currently, Azure HDInsight on AKS doesn't support availability zone in its service offerings.
+Azure HDInsight on AKS supports availability zone by leveraging Azure Kubernetes Service's ability to create zone redundant node pools. You can select which availability zones to deploy the cluster pool and cluster during their creation. Once the cluster pool or cluster are created, you can't change the availability zones.
+
+### Prerequisites
+
+- Availability zones are only supported for cluster pool version >= `1.2` and cluster version >= `1.2.1`.
+- Azure HDInsight on AKS only has one default SKU and it supports AZ as long as the Azure region has AZ support.
+
+  Below regions don't support AZ:
+
+  | Americas         | Europe               | Middle East   | Africa             | Asia Pacific   |
+  |------------------|----------------------|---------------|--------------------|----------------|
+  | West US          | Germany North        |               |                    |                |
+- Some VM SKUs may not support all availability zones in a region. If you select those SKUs, HDInsight on AKS cluster pools or clusters don't support corresponding availability zones either.
+
+### SLA improvements
+
+There are no increased SLAs for Azure HDInsight on AKS clusters with availability zones enabled.
+
+#### Create a resource with availability zone enabled
+
+- Cluster Pools
+  You can select one or more availability zones during cluster pool creation after you select the region.
+
+- Clusters
+  You can select one or more availability zones during cluster creation.
+
+### Fault tolerance
+
+To prepare for availability zone failure, it's recommended to over-provision capacity of service to ensure that your cluster can tolerate the loss of capacity from one availability zone down and continue to function without degraded performance during zone-wide outages. For instance, if you enable 3 availability zones, your cluster should tolerate 1/3 of the nodes down (round up to the nearest integer).
+
+### Zone down experience
+
+Azure HDInsight on AKS service is zone redundant. During a zone-wide outage, the customer should expect degradation of performance due to capacity drop. Customers can still create new cluster pools and clusters in the availability zones that are not impacted. Existing clusters can function with reduced capacity.
 
 ## Disaster recovery and business continuity