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Copy file name to clipboardExpand all lines: articles/app-service/routine-maintenance.md
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# Routine (planned) maintenance for App Service
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Routine maintenance is a term which covers behind the scenes changes in the platform. Types of maintenance can be performance improvements, bug fixes,
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new features, or security updates. Since App Service is a managed platform and consists of multiple layers of the stack, all those said changes can be in both service itself (Azure App Service) and the underlying OS (both Windows and Linux) of individual machines used to run the service.
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Routine maintenance covers behind the scenes updates to the Azure App Service platform. Types of maintenance can be performance improvements, bug fixes,
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new features, or security updates. App Service maintenance can be on App Service itself or the underlying operating system.
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>[IMPORTANT!]
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>A breaking change or deprecation of functionality is not a part of routine maintenance (see [Modern Lifecycle Policy - Microsoft Lifecycle | Microsoft Learn](/lifecycle/policies/modern) for deprecation topic for details).
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## What to expect
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Like security updates on personal computers, mobile phones and other devices, even machines in the cloud need the latest updates. Unlike physical devices, cloud solutions like Azure App Service provide ways to overcome these routines with more ease. There's no need to "stop working" for a certain period and wait until patches are installed. Any workload can be just shifted to a different underlying hardware in a matter of seconds and while updates are installed. The updates are made monthly, but can vary on the needs and other factors.
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Like security updates on personal computers, mobile phones and other devices, even machines in the cloud need the latest updates. Unlike physical devices, cloud solutions like Azure App Service provide ways to overcome these routines with more ease. There's no need to "stop working" for a certain period and wait until patches are installed. Any workload can be shifted to different hardware in a matter of seconds and while updates are installed. The updates are made monthly, but can vary on the needs and other factors.
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Since a typical cloud solution consists of multiple applications, databases, storage accounts, functions, and other resources, various parts of your solutions can be undergoing maintenance at different times. Some of this coordination is related to placements (geographies, regions, data centers, availability zones) and some of this is due to a pure scale of the cloud where not everything is touched simultaneously.
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Since a typical cloud solution consists of multiple applications, databases, storage accounts, functions, and other resources, various parts of your solutions can be undergoing maintenance at different times. Some of this coordination is related to geography, region, data centers, and availability zones. It can also be due to the cloud where not everything is touched simultaneously.
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[Safe deployment practices - Azure DevOps | Microsoft Learn](/devops/operate/safe-deployment-practices)
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### Why am I getting so many notifications?
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A typical scenario is that customers have multiple applications, and they are upgraded at different times. To avoid sending notifications for each of them, a more generic notification is provided that captures multiple resources. The notification is sent at the beginning and throughout the maintenance window. Due to the time window being longer, you can receive multiple reminders for the same rollout so you can easier correlate any restart/interruption/issue in case it is needed.
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A typical scenario is that customers have multiple applications, and they are upgraded at different times. To avoid sending notifications for each of them, a more generic notification is sent that captures multiple resources. The notification is sent at the beginning and throughout the maintenance window. Due to the time window being longer, you can receive multiple reminders for the same rollout so you can easier correlate any restart/interruption/issue in case it is needed.
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### How is this related to SLA, is the uptime factored in or not?
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### How is routine maintenance related to SLA?
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Platform maintenance isn't expected to impact application uptime or availability. Applications continue to stay online while platform maintenance occurs. Platform maintenance may cause applications to be cold started on new virtual machines, which can lead to cold start delays. An application is still considered to be online, , even while cold-starting. For best practices to minimize/avoid cold starts, consider using [local cache for Windows apps](overview-local-cache.md) as well as [Health check](monitor-instances-health-check.md). It's not expected that sites would incur any SLA violation during maintenance windows.
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### How does the upgrade work under the hood and how does it ensure smooth operation for my apps?
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### How does the upgrade work how does it ensure the smooth operation of my apps?
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Azure App Service represents a fleet of scale units which provide hosting of web applications/solutions to the customers. Each scale unit is further divided into smaller pieces (roles of different purposes) and sliced into a concept of upgrade domains (and availability zones) to optimize placements of bigger App Service Plans and smooth deployments since not all machines in each scale unit are updated at once. Fleet upgrades machines iteratively while monitoring the health of the fleet so any time there is an issue, the system can stop the rollout. This is described in detail at [Demystifying the magic behind App Service OS updates - Azure App Service](https://azure.github.io/AppService/2018/01/18/Demystifying-the-magic-behind-App-Service-OS-updates.html).
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Azure App Service represents a fleet of scale units, which provide hosting of web applications/solutions to the customers. Each scale unit is further divided into smaller pieces and sliced into a concept of upgrade domains and availability zones. This is to optimize placements of bigger App Service Plans and smooth deployments since not all machines in each scale unit are updated at once. Fleet upgrades machines iteratively while monitoring the health of the fleet so any time there is an issue, the system can stop the rollout. This process is described in detail at [Demystifying the magic behind App Service OS updates - Azure App Service](https://azure.github.io/AppService/2018/01/18/Demystifying-the-magic-behind-App-Service-OS-updates.html).
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### Are business hours reflected?
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Maintenance operations are optimized to run outside standard business hours (9-5pm) as statistically that is a better timing for any interruptions and restarts of workloads as there is a less stress on the system (in customer applications and transitively also on the platform itself).
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### What are my options to control this?
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### What are my options to control routine maintenance?
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If you run your workloads in Isolated SKU via App Service Environment v3, you can also schedule the upgrades when needed. This is described with details at Control and automate planned maintenance for App Service Environment v3 - Azure App Service .
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### Can I prepare my apps better for restarts?
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If your applications need extra time during restarts to come online (a typical pattern would be heavy dependency on external resources during application warm-up/start-up), consider using [Health Check](monitor-instances-health-check.md). You can use this to communicate with the platform that your application is not ready to receive requests yet and the system can use that information to route requests to other instances in your App Service Plan (for such case, it is recommended to have at least 2 instances in the plan).
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If your applications need extra time during restarts to come online (a typical pattern would be heavy dependency on external resources during application warm-up/start-up), consider using [Health Check](monitor-instances-health-check.md). You can use this to communicate with the platform that your application is not ready to receive requests yet and the system can use that information to route requests to other instances in your App Service Plan. For such case, it's recommended to have at least two instances in the plan.
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### My applications have been running fine but since these notifications started showing up things are worse. What changed?
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### My applications have been online, but since these notifications started showing up things are worse. What changed?
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Updates and maintenance events have been happening to the platform since its inception. The frequency of updates decreased over time, so the number of interruptions also decreased and uptime increases. However, there is an increased level of visibility into all changes which can cause the perception that more changes are being made.
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