Merge pull request #300461 from johndowns/reliability-service-maintenance-app-service

Reliability Hub - App Service - Add 'Reliability during service maintenance' section

Author: prmerger-automator[bot]

articles/reliability/reliability-app-service.md

@@ -45,8 +45,6 @@ Microsoft-provided SDKs usually handle transient faults. Because you host your o
 
 - **Deploy multiple instances in your plan.**  Azure App Service performs automated updates and other forms of maintenance on instances in your plan. If an instance becomes unhealthy, the service can automatically replace that instance with a new healthy instance. During the replacement process, there can be a short period when the previous instance is unavailable and a new instance isn't yet ready to serve traffic. You can mitigate the impact of this behavior by deploying multiple instances of your App Service plan.
 
-    When you enable zone redundancy on your App Service plan, you also improve your resiliency to updates that the App Service platform rolls out. *Update domains* consist of collections of virtual machines (VMs) that are taken offline at the time of an update. Update domains are tied to availability zones. Deploying multiple instances in your App Service plan and enabling zone redundancy for your plan adds an extra layer of resiliency during upgrades if an instance or zone becomes unhealthy.
-
 - **Use deployment slots.** Azure App Service [deployment slots](/azure/app-service/deploy-staging-slots) allow for zero-downtime deployments of your applications. Use deployment slots to minimize the impact of deployments and configuration changes for your users. Using deployment slots also reduces the likelihood that your application restarts. Restarting causes a transient fault.
 
 - **Avoid scaling up or down.** Instead, select a tier and instance size that meet your performance requirements under typical load. Only scale out instances to handle changes in traffic volume. Scaling up and down can trigger an application restart.
@@ -133,6 +131,8 @@ To see which regions support availability zones for App Service Environment v3,
 
 During an availability zone outage, some aspects of Azure App Service might be impacted even though the application continues to serve traffic. These behaviors include App Service plan scaling, application creation, application configuration, and application publishing.
 
+When you enable zone redundancy on your App Service plan, you also improve your resiliency to updates that the App Service platform rolls out. To learn more, see [Reliability during service maintenance](#reliability-during-service-maintenance).
+
 ### Cost
 
 ::: zone-end
@@ -420,6 +420,26 @@ When you use Basic tier or higher, you can back up your App Service app to a fil
 
 This feature is useful if it's hard to redeploy your code, or if you store state on disk. For most solutions, you shouldn't rely on App Service backups. Use the other methods described in this article to support your resiliency requirements.
 
+## Reliability during service maintenance
+
+Azure App Service performs regular service upgrades, as well as other forms of maintenance. To ensure that your expected capacity is available during an upgrade, the platform automatically adds extra instances of the App Service plan during the upgrade process.
+
+**Enable zone redundancy.** When you enable zone redundancy on your App Service plan, you also improve your resiliency to updates that the App Service platform rolls out. *Update domains* consist of collections of virtual machines (VMs) that are taken offline at the time of an update. Update domains are tied to availability zones. Deploying multiple instances in your App Service plan and enabling zone redundancy for your plan adds an extra layer of resiliency during upgrades if an instance or zone becomes unhealthy.
+
+::: zone pivot="free-shared-basic,premium"
+
+To learn more, see [Routine planned maintenance for Azure App Service](/azure/app-service/routine-maintenance).
+
+::: zone-end
+
+::: zone pivot="isolated"
+
+**Customize the upgrade cycle.** You to customize the upgrade cycle for an App Service Environment. If you need to validate the effect of upgrades on your workload, consider enabling manual upgrades so you can perform validation and testing on a nonproduction instance before the change rolls out to your production instance.
+
+To learn more about maintenance preferences, see [Upgrade preference for App Service Environment planned maintenance](/azure/app-service/environment/how-to-upgrade-preference).
+
+::: zone-end
+
 ## Service-level agreement (SLA)
 
 The service-level agreement (SLA) for Azure App Service describes the expected availability of the service. It also describes the conditions that must be met to achieve that availability expectation. To understand those conditions, review the [Service Level Agreements (SLA) for Online Services](https://www.microsoft.com/licensing/docs/view/Service-Level-Agreements-SLA-for-Online-Services).