Merge pull request #104777 from stefsch/patch-15

Minor tweaks to align with overall Azure guidance on AZs

Author: ShannonLeavitt

articles/reliability/migrate-app-service.md

@@ -22,7 +22,7 @@ An App Service lives in an App Service plan (ASP), and the App Service plan exis
 
 - For App Services that aren't configured to be zone redundant, the VM instances are placed in a single zone that is selected by the platform in the selected region.
 
-- For App Services that are configured to be zone redundant, the platform automatically spreads the VM instances in the App Service plan across all three zones in the selected region. If a VM instance capacity larger than three is specified and the number of instances is a multiple of three (3 * N), the instances will be spread evenly. However, if the number of instances is not a multiple of three, the remainder of the instances will get spread across the remaining one or two zones.
+- For App Services that are configured to be zone redundant, the platform automatically spreads the VM instances in the App Service plan across three zones in the selected region. If a VM instance capacity larger than three is specified and the number of instances is a multiple of three (3 * N), the instances will be spread evenly. However, if the number of instances is not a multiple of three, the remainder of the instances will get spread across the remaining one or two zones.
 
 > [!NOTE]
 > [App Service SLA](https://www.microsoft.com/licensing/docs/view/Service-Level-Agreements-SLA-for-Online-Services?lang=1) is calculated based on the Maximum Available Minutes and Downtime which is standard irrespective of availability zone enablement. Downtime for the App Service is defined as the following.
@@ -81,7 +81,7 @@ If you want your App Service to use availability zones, redeploy your apps into
 
 Traffic is routed to all of your available App Service instances. In the case when a zone goes down, the App Service platform will detect lost instances and automatically attempt to find new replacement instances and spread traffic as needed. If you have [autoscale](../app-service/manage-scale-up.md) configured, and if it decides more instances are needed, autoscale will also issue a request to App Service to add more instances. Note that [autoscale behavior is independent of App Service platform behavior](../azure-monitor/autoscale/autoscale-overview.md) and that your autoscale instance count specification doesn't need to be a multiple of three. It's also important to note there's no guarantee that requests for additional instances in a zone-down scenario will succeed since back filling lost instances occurs on a best-effort basis. The recommended solution is to create and configure your App Service plans to account for losing a zone as described in the next section.
 
-Applications that are deployed in an App Service plan that has availability zones enabled will continue to run and serve traffic even if other zones in the same region suffer an outage. However it's possible that non-runtime behaviors including App Service plan scaling, application creation, application configuration, and application publishing may still be impacted from an outage in other Availability Zones. Zone redundancy for App Service plans only ensures continued uptime for deployed applications.
+Applications that are deployed in an App Service plan that has availability zones enabled will continue to run and serve traffic if a single zone becomes unavailable. However it's possible that non-runtime behaviors including App Service plan scaling, application creation, application configuration, and application publishing may still be impacted from an outage in other Availability Zones. Zone redundancy for App Service plans only ensures continued uptime for deployed applications.
 
 When the App Service platform allocates instances to a zone redundant App Service plan, it uses [best effort zone balancing offered by the underlying Azure Virtual Machine Scale Sets](../virtual-machine-scale-sets/virtual-machine-scale-sets-use-availability-zones.md#zone-balancing). An App Service plan will be "balanced" if each zone has either the same number of VMs, or +/- one VM in all of the other zones used by the App Service plan.