Add doc for availabilty zones

Author: ArchangelSDY

articles/azure-signalr/TOC.yml

@@ -65,6 +65,8 @@
       href: server-graceful-shutdown.md
     - name: Resiliency and disaster recovery
       href: signalr-concept-disaster-recovery.md
+    - name: Availability zones
+      href: availability-zones.md
   - name: Messages and connections
     href: signalr-concept-messages-and-connections.md
   - name: Performance considerations

articles/azure-signalr/availability-zones.md

@@ -0,0 +1,29 @@
+---
+title: Availability zones support in Azure SignalR Service
+description: Availability zones support in Azure SignalR Service
+author: ArchangelSDY
+ms.service: signalr
+ms.topic: conceptual
+ms.date: 02/15/2022
+ms.author: dayshen
+---
+# Availability zones support in Azure SignalR Service
+
+[Availability zones](../availability-zones/az-overview.md#availability-zones) are unique physical locations within an Azure region. To ensure resiliency, there's a minimum of three separate zones in all enabled regions. Each zone has one or more datacenters equipped with independent power, cooling, and networking.
+
+## Zone redundancy
+
+Azure SignalR Service leverages availability zones in a Zone Redundant manner. That means, the service doesn't spin to a specific zone. Instead workloads are evenly distributed across multiple zones in a region. When a single zone fails, traffic are automatically routed to other zones, keeping the service available.
+
+## Region support
+
+Not all Azure regions support availability zones. For the regions list, see [regions that support availability zones](../availability-zones/az-region.md).
+
+## Tier support
+
+Zone redundancy is a Premium tier feature. It is implicitly enabled when you create or upgrade to a Premium tier resource. Standard tier resources can be upgraded to Premium tier without downtime.
+
+## Next steps
+
+* Learn more about [regions that support availability zones](../availability-zones/az-region.md).
+* Learn more about building for [reliability](/azure/architecture/framework/resiliency/app-design) in Azure.