Azure Virtual Machine Scale Set automatic OS image upgrades

Enabling automatic OS image upgrades on your scale set helps ease update management by safely and automatically upgrading the OS disk for all instances in the scale set.

Automatic OS upgrade has the following characteristics:

• Once configured, the latest OS image published by image publishers is automatically applied to the scale set without user intervention.
• Upgrades batches of instances in a rolling manner each time a new image is published by the publisher.
• Integrates with application health probes and Application Health extension.
• Works for all VM sizes, and for both Windows and Linux images including custom images through Azure Compute Gallery.
• You can opt out of automatic upgrades at any time (OS Upgrades can be initiated manually as well).
• The OS Disk of a VM is replaced with the new OS Disk created with latest image version. Configured extensions and custom data scripts are run, while persisted data disks are retained.
• Extension sequencing is supported.
• Can be enabled on a scale set of any size.

How does automatic OS image upgrade work?

An upgrade works by replacing the OS disk of a VM with a new disk created using the image version. Any configured extensions and custom data scripts are run on the OS disk, while data disks are retained. To minimize the application downtime, upgrades take place in batches, with no more than 20% of the scale set upgrading at any time.

You must integrate an Azure Load Balancer application health probe or Application Health extension to track the health of the application after an upgrade. This allows the platform to validate the VM health to ensure updates are applied in a safe manner. We recommend incorporating an application heartbeat to validate upgrade success.

Availability-first Updates

The availability-first model for platform orchestrated updates described below ensures that availability configurations in Azure are respected across multiple availability levels.

Across regions:

• An update will move across Azure globally in a phased manner to prevent Azure-wide deployment failures.
• A 'phase' can have one or more regions, and an update moves across phases only if eligible VMs in the previous phase update successfully.
• Geo-paired regions will not be updated concurrently and cannot be in the same regional phase.
• The success of an update is measured by tracking the health of a VM post update.

Within a region:

• VMs in different Availability Zones are not updated concurrently with the same update.

Within a 'set':

• All VMs in a common scale set are not updated concurrently.
• VMs in a common Virtual Machine Scale Set are grouped in batches and updated within Update Domain boundaries as described below.

The platform orchestrated updates process is followed for rolling out supported OS platform image upgrades every month. For custom images through Azure Compute Gallery, an image upgrade is only kicked off for a particular Azure region when the new image is published and replicated to the region of that scale set.

Upgrading VMs in a scale set

The region of a scale set becomes eligible to get image upgrades either through the availability-first process for platform images or replicating new custom image versions for Share Image Gallery. The image upgrade is then applied to an individual scale set in a batched manner as follows:

1. Before you begin the upgrade process, the orchestrator will ensure that no more than 20% of instances in the entire scale set are unhealthy (for any reason).
2. The upgrade orchestrator identifies the batch of VM instances to upgrade, with any one batch having a maximum of 20% of the total instance count, subject to a minimum batch size of one virtual machine. There is no minimum scale set size requirement and scale sets with 5 or fewer instances will have 1 VM per upgrade batch (minimum batch size).
3. The OS disk of every VM in the selected upgrade batch is replaced with a new OS disk created from the image. All specified extensions and configurations in the scale set model are applied to the upgraded instance.
4. For scale sets with configured application health probes or Application Health extension, the upgrade waits up to 5 minutes for the instance to become healthy, before moving on to upgrade the next batch. If an instance does not recover its health in 5 minutes after an upgrade, then by default the previous OS disk for the instance is restored.
5. The upgrade orchestrator also tracks the percentage of instances that become unhealthy post an upgrade. The upgrade will stop if more than 20% of upgraded instances become unhealthy during the upgrade process.
6. The above process continues until all instances in the scale set have been upgraded.

The scale set OS upgrade orchestrator checks for the overall scale set health before upgrading every batch. While you're upgrading a batch, there could be other concurrent planned or unplanned maintenance activities that could impact the health of your scale set instances. In such cases if more than 20% of the scale set's instances become unhealthy, then the scale set upgrade stops at the end of current batch.

To modify the default settings associated with Rolling Upgrades, review Azure's Rolling Upgrade Policy.

OS image upgrade versus reimage

Both OS Image Upgrade and Reimage are methods used to update VMs within a scale set, but they serve different purposes and have distinct impacts.

OS image upgrade involves updating the underlying operating system image that is used to create new instances in a scale set. When you perform an OS image upgrade, Azure will create new VM instances with the updated OS image and gradually replace the old VM instances in the scale set with the new ones. This process is typically performed in stages to ensure high availability. OS image upgrades are a non-disruptive way to apply updates or changes to the underlying OS of the VMs in a scale set. Existing VM instances are not affected until they are replaced with the new instances.

Reimaging a VM instance in a scale set is a more immediate and disruptive action. When you choose to reimage a VM instance, Azure will stop the selected VM instance, perform the reimage operation, and then restart the VM using the same OS image. This effectively reinstalls the OS on that specific VM instance. Reimaging is typically used when you need to troubleshoot or reset a specific VM instance due to issues with that instance.

Key differences:

• OS Image Upgrade is a gradual and non-disruptive process that updates the OS image for the entire Virtual Machine Scale Set over time, ensuring minimal impact on running workloads.
• Reimage is a more immediate and disruptive action that affects only the selected VM instance, stopping it temporarily and reinstalling the OS.

When to use each method:

• Use OS Image Upgrade when you want to update the OS image for the entire scale set while maintaining high availability.
• Use Reimage when you need to troubleshoot or reset a specific VM instance within the virtual Machine Scale Set.

It's essential to carefully plan and choose the appropriate method based on your specific requirements to minimize any disruption to your applications and services running in a Virtual Machine Scale Set.

Supported OS images

Only certain OS platform images are currently supported. Custom images are supported if the scale set uses custom images through Azure Compute Gallery.

The following platform SKUs are currently supported (and more are added periodically):

Publisher	OS Offer	Sku
Canonical	UbuntuServer	18.04-LTS
Canonical	UbuntuServer	18_04-LTS-Gen2
Canonical	0001-com-ubuntu-server-focal	20_04-LTS
Canonical	0001-com-ubuntu-server-focal	20_04-LTS-Gen2
Canonical	0001-com-ubuntu-server-jammy	22_04-LTS
Canonical	0001-com-ubuntu-server-jammy	22_04-LTS-Gen2
MicrosoftCblMariner	Cbl-Mariner	cbl-mariner-1
MicrosoftCblMariner	Cbl-Mariner	1-Gen2
MicrosoftCblMariner	Cbl-Mariner	cbl-mariner-2
MicrosoftCblMariner	Cbl-Mariner	cbl-mariner-2-Gen2
MicrosoftSqlServer	Sql2017-ws2019	enterprise
MicrosoftWindowsServer	WindowsServer	2012-R2-Datacenter
MicrosoftWindowsServer	WindowsServer	2016-Datacenter
MicrosoftWindowsServer	WindowsServer	2016-Datacenter-gensecond
MicrosoftWindowsServer	WindowsServer	2016-Datacenter-gs
MicrosoftWindowsServer	WindowsServer	2016-Datacenter-smalldisk
MicrosoftWindowsServer	WindowsServer	2016-Datacenter-with-Containers
MicrosoftWindowsServer	WindowsServer	2016-Datacenter-with-containers-gs
MicrosoftWindowsServer	WindowsServer	2019-Datacenter
MicrosoftWindowsServer	WindowsServer	2019-Datacenter-Core
MicrosoftWindowsServer	WindowsServer	2019-Datacenter-Core-with-Containers
MicrosoftWindowsServer	WindowsServer	2019-Datacenter-gensecond
MicrosoftWindowsServer	WindowsServer	2019-Datacenter-gs
MicrosoftWindowsServer	WindowsServer	2019-Datacenter-smalldisk
MicrosoftWindowsServer	WindowsServer	2019-Datacenter-with-Containers
MicrosoftWindowsServer	WindowsServer	2019-Datacenter-with-Containers-gs
MicrosoftWindowsServer	WindowsServer	2022-Datacenter
MicrosoftWindowsServer	WindowsServer	2022-Datacenter-smalldisk
MicrosoftWindowsServer	WindowsServer	2022-Datacenter-smalldisk-g2
MicrosoftWindowsServer	WindowsServer	2022-Datacenter-core
MicrosoftWindowsServer	WindowsServer	2022-Datacenter-core-smalldisk
MicrosoftWindowsServer	WindowsServer	2022-Datacenter-g2
MicrosoftWindowsServer	WindowsServer	Datacenter-core-20h2-with-containers-smalldisk-gs
MicrosoftWindowsServer	WindowsServer	2022-Datacenter-azure-edition
MicrosoftWindowsServer	WindowsServer	2022-Datacenter-azure-edition-smalldisk
Mirantis	Windows_with_Mirantis_Container_Runtime_2019	win_2019_mcr_23_0
Mirantis	Windows_with_Mirantis_Container_Runtime_2019	win_2019_mcr_23_0_gen2

Requirements for configuring automatic OS image upgrade

• The version property of the image must be set to latest.
• Must use application health probes or Application Health extension for non-Service Fabric scale sets. For Service Fabric requirements, see Service Fabric requirement.
• Use Compute API version 2018-10-01 or higher.
• Ensure that external resources specified in the scale set model are available and updated. Examples include SAS URI for bootstrapping payload in VM extension properties, payload in storage account, reference to secrets in the model, and more.
• For scale sets using Windows virtual machines, starting with Compute API version 2019-03-01, the virtualMachineProfile.osProfile.windowsConfiguration.enableAutomaticUpdates property must set to false in the scale set model definition. The enableAutomaticUpdates property enables in-VM patching where "Windows Update" applies operating system patches without replacing the OS disk. With automatic OS image upgrades enabled on your scale set, which can be done by setting the automaticOSUpgradePolicy.enableAutomaticOSUpgrade to true, an extra patching process through Windows Update is not required.
• The patch orchestration mode must not be set to AutomaticByPlatform in the scale set model definition. With automatic OS image upgrades enabled on your scale set, a platform orchestration patching process is not required.

Service Fabric requirements

If you are using Service Fabric, ensure the following conditions are met:

• Service Fabric durability level is Silver or Gold. If Service Fabric durability is Bronze, only Stateless-only node types support automatic OS image upgrades).
• The Service Fabric extension on the scale set model definition must have TypeHandlerVersion 1.1 or above.
• Durability level should be the same at the Service Fabric cluster and Service Fabric extension on the scale set model definition.
• An additional health probe or use of application health extension is not required for Silver or Gold durability. Bronze durability with Stateless-only node types requires an additional health probe.
• The property virtualMachineProfile.osProfile.windowsConfiguration.enableAutomaticUpdates property must set to false in the scale set model definition. The enableAutomaticUpdates property enables in-VM patching using "Windows Update" and is not supported on Service Fabric scale sets. You should use the automaticOSUpgradePolicy.enableAutomaticOSUpgrade property instead.

Ensure that durability settings are not mismatched on the Service Fabric cluster and Service Fabric extension, as a mismatch will result in upgrade errors. Durability levels can be modified per the guidelines outlined on this page.

Automatic OS image upgrade for custom images

Automatic OS image upgrade is supported for custom images deployed through Azure Compute Gallery. Other custom images are not supported for automatic OS image upgrades.

Additional requirements for custom images

• The setup and configuration process for automatic OS image upgrade is the same for all scale sets as detailed in the configuration section of this page.
• Scale sets instances configured for automatic OS image upgrades will be upgraded to the version of the Azure Compute Gallery image when a new version of the image is published and replicated to the region of that scale set. If the new image is not replicated to the region where the scale is deployed, the scale set instances will not be upgraded to the version. Regional image replication allows you to control the rollout of the new image for your scale sets.
• The new image version should not be excluded from the version for that gallery image. Image versions excluded from the gallery image's version are not rolled out to the scale set through automatic OS image upgrade.

Configure automatic OS image upgrade

To configure automatic OS image upgrade, ensure that the automaticOSUpgradePolicy.enableAutomaticOSUpgrade property is set to true in the scale set model definition.

REST API

The following example describes how to set automatic OS upgrades on a scale set model:

PUT or PATCH on `/subscriptions/subscription_id/resourceGroups/myResourceGroup/providers/Microsoft.Compute/virtualMachineScaleSets/myScaleSet?api-version=2021-03-01`

{
  "properties": {
    "upgradePolicy": {
      "automaticOSUpgradePolicy": {
        "enableAutomaticOSUpgrade":  true
      }
    }
  }
}

Azure PowerShell

Use the New-AzVmss cmdlet to configure automatic OS image upgrades for your scale set during provisioning. The following example configures automatic upgrades for the scale set named myScaleSet in the resource group named myResourceGroup:

New-AzVmss -ResourceGroupName "myResourceGroup" -VMScaleSetName "myScaleSet" -AutomaticOSUpgrade $true

Use the Update-AzVmss cmdlet to configure automatic OS image upgrades for your existing scale set. The following example configures automatic upgrades for the scale set named myScaleSet in the resource group named myResourceGroup:

Update-AzVmss -ResourceGroupName "myResourceGroup" -VMScaleSetName "myScaleSet" -AutomaticOSUpgrade $true

Azure CLI 2.0

Use az vmss create to configure automatic OS image upgrades for your scale set during provisioning. Use Azure CLI 2.0.47 or above. The following example configures automatic upgrades for the scale set named myScaleSet in the resource group named myResourceGroup:

az vmss create --name myScaleSet --resource-group myResourceGroup --enable-auto-os-upgrade true --upgrade-policy-mode Rolling

Use az vmss update to configure automatic OS image upgrades for your existing scale set. Use Azure CLI 2.0.47 or above. The following example configures automatic upgrades for the scale set named myScaleSet in the resource group named myResourceGroup:

az vmss update --name myScaleSet --resource-group myResourceGroup --enable-auto-os-upgrade true --upgrade-policy-mode Rolling

ARM templates

The following example describes how to set automatic OS upgrades on a scale set model via Azure Resource Manager templates (ARM templates):

"properties": {
   "upgradePolicy": {
     "mode": "Automatic",
     "RollingUpgradePolicy": {
         "BatchInstancePercent": 20,
         "MaxUnhealthyInstancePercent": 25,
         "MaxUnhealthyUpgradedInstancePercent": 25,
         "PauseTimeBetweenBatches": "PT0S"
     },
    "automaticOSUpgradePolicy": {
      "enableAutomaticOSUpgrade": true,
        "useRollingUpgradePolicy": true,
        "disableAutomaticRollback": false
    }
  },
  },
"imagePublisher": {
   "type": "string",
   "defaultValue": "MicrosoftWindowsServer"
 },
 "imageOffer": {
   "type": "string",
   "defaultValue": "WindowsServer"
 },
 "imageSku": {
   "type": "string",
   "defaultValue": "2022-datacenter"
 },
 "imageOSVersion": {
   "type": "string",
   "defaultValue": "latest"
 }

Bicep

The following example describes how to set automatic OS upgrades on a scale set model via Bicep:

properties: {
    overprovision: overProvision
    upgradePolicy: {
      mode: 'Automatic'
      automaticOSUpgradePolicy: {
        enableAutomaticOSUpgrade: true
      }
    }
}

Using Application Health Extension

During an OS Upgrade, VM instances in a scale set are upgraded one batch at a time. The upgrade should continue only if the customer application is healthy on the upgraded VM instances. We recommend that the application provides health signals to the scale set OS Upgrade engine. By default, during OS Upgrades the platform considers VM power state and extension provisioning state to determine if a VM instance is healthy after an upgrade. During the OS Upgrade of a VM instance, the OS disk on a VM instance is replaced with a new disk based on latest image version. After the OS Upgrade has completed, the configured extensions are run on these VMs. The application is considered healthy only when all the extensions on the instance are successfully provisioned.

A scale set can optionally be configured with Application Health Probes to provide the platform with accurate information on the ongoing state of the application. Application Health Probes are Custom Load Balancer Probes that are used as a health signal. The application running on a scale set VM instance can respond to external HTTP or TCP requests indicating whether it's healthy. For more information on how Custom Load Balancer Probes work, see to Understand load balancer probes. Application Health Probes are not supported for Service Fabric scale sets. Non-Service Fabric scale sets require either Load Balancer application health probes or Application Health extension.

If the scale set is configured to use multiple placement groups, probes using a Standard Load Balancer need to be used.

Configuring a Custom Load Balancer Probe as Application Health Probe on a scale set

As a best practice, create a load balancer probe explicitly for scale set health. The same endpoint for an existing HTTP probe or TCP probe can be used, but a health probe could require different behavior from a traditional load-balancer probe. For example, a traditional load balancer probe could return unhealthy if the load on the instance is too high, but that would not be appropriate for determining the instance health during an automatic OS upgrade. Configure the probe to have a high probing rate of less than two minutes.

The load-balancer probe can be referenced in the networkProfile of the scale set and can be associated with either an internal or public facing load-balancer as follows:

"networkProfile": {
  "healthProbe" : {
    "id": "[concat(variables('lbId'), '/probes/', variables('sshProbeName'))]"
  },
  "networkInterfaceConfigurations":
  ...
}

Using Application Health extension

The Application Health extension is deployed inside a Virtual Machine Scale Set instance and reports on VM health from inside the scale set instance. You can configure the extension to probe on an application endpoint and update the status of the application on that instance. This instance status is checked by Azure to determine whether an instance is eligible for upgrade operations.

As the extension reports health from within a VM, the extension can be used in situations where external probes such as Application Health Probes (that utilize custom Azure Load Balancer probes) can’t be used.

There are multiple ways of deploying the Application Health extension to your scale sets as detailed in the examples in this article.

Get the history of automatic OS image upgrades

You can check the history of the most recent OS upgrade performed on your scale set with Azure PowerShell, Azure CLI 2.0, or the REST APIs. You can get history for the last five OS upgrade attempts within the past two months.

Keep credentials up to date

If your scale set uses any credentials to access external resources, such as a VM extension configured to use a SAS token for storage account, then ensure that the credentials are updated. If any credentials, including certificates and tokens, have expired, the upgrade will fail and the first batch of VMs will be left in a failed state.

The recommended steps to recover VMs and re-enable automatic OS upgrade if there's a resource authentication failure are:

• Regenerate the token (or any other credentials) passed into your extension(s).
• Ensure that any credential used from inside the VM to talk to external entities is up to date.
• Update extension(s) in the scale set model with any new tokens.
• Deploy the updated scale set, which will update all VM instances including the failed ones.

REST API

The following example uses REST API to check the status for the scale set named myScaleSet in the resource group named myResourceGroup:

GET on `/subscriptions/subscription_id/resourceGroups/myResourceGroup/providers/Microsoft.Compute/virtualMachineScaleSets/myScaleSet/osUpgradeHistory?api-version=2021-03-01`

The GET call returns properties similar to the following example output:

{
	"value": [
		{
			"properties": {
        "runningStatus": {
          "code": "RollingForward",
          "startTime": "2018-07-24T17:46:06.1248429+00:00",
          "completedTime": "2018-04-21T12:29:25.0511245+00:00"
        },
        "progress": {
          "successfulInstanceCount": 16,
          "failedInstanceCount": 0,
          "inProgressInstanceCount": 4,
          "pendingInstanceCount": 0
        },
        "startedBy": "Platform",
        "targetImageReference": {
          "publisher": "MicrosoftWindowsServer",
          "offer": "WindowsServer",
          "sku": "2016-Datacenter",
          "version": "2016.127.20180613"
        },
        "rollbackInfo": {
          "successfullyRolledbackInstanceCount": 0,
          "failedRolledbackInstanceCount": 0
        }
      },
      "type": "Microsoft.Compute/virtualMachineScaleSets/rollingUpgrades",
      "location": "chinanorth2"
    }
  ]
}

Azure PowerShell

Use the Get-AzVmss cmdlet to check OS upgrade history for your scale set. The following example details how you review the OS upgrade status for a scale set named myScaleSet in the resource group named myResourceGroup:

Get-AzVmss -ResourceGroupName "myResourceGroup" -VMScaleSetName "myScaleSet" -OSUpgradeHistory

Azure CLI 2.0

Use az vmss get-os-upgrade-history to check the OS upgrade history for your scale set. Use Azure CLI 2.0.47 or above. The following example details how you review the OS upgrade status for a scale set named myScaleSet in the resource group named myResourceGroup:

az vmss get-os-upgrade-history --resource-group myResourceGroup --name myScaleSet

How to get the latest version of a platform OS image?

You can get the available image versions for automatic OS upgrade supported SKUs using the below examples:

REST API

GET on `/subscriptions/subscription_id/providers/Microsoft.Compute/locations/{location}/publishers/{publisherName}/artifacttypes/vmimage/offers/{offer}/skus/{skus}/versions?api-version=2021-03-01`

Azure PowerShell

Get-AzVmImage -Location "chinanorth2" -PublisherName "Canonical" -offer "0001-com-ubuntu-server-jammy" -sku "22_04-lts"

Azure CLI 2.0

az vm image list --location "chinanorth2" --publisher "Canonical" --offer "0001-com-ubuntu-server-jammy" --sku "22_04-lts" --all

Manually trigger OS image upgrades

With automatic OS image upgrade enabled on your scale set, you do not need to manually trigger image updates on your scale set. The OS upgrade orchestrator will automatically apply the latest available image version to your scale set instances without any manual intervention.

For specific cases where you do not want to wait for the orchestrator to apply the latest image, you can trigger an OS image upgrade manually using the below examples.

REST API

Use the Start OS Upgrade API call to start a rolling upgrade to move all Virtual Machine Scale Set instances to the latest available image OS version. Instances that are already running the latest available OS version are not affected. The following example details how you can start a rolling OS upgrade on a scale set named myScaleSet in the resource group named myResourceGroup:

POST on `/subscriptions/subscription_id/resourceGroups/myResourceGroup/providers/Microsoft.Compute/virtualMachineScaleSets/myScaleSet/osRollingUpgrade?api-version=2021-03-01`

Azure PowerShell

Use the Start-AzVmssRollingOSUpgrade cmdlet to check OS upgrade history for your scale set. The following example details how you can start a rolling OS upgrade on a scale set named myScaleSet in the resource group named myResourceGroup:

Start-AzVmssRollingOSUpgrade -ResourceGroupName "myResourceGroup" -VMScaleSetName "myScaleSet"

Azure CLI 2.0

Use az vmss rolling-upgrade start to check the OS upgrade history for your scale set. Use Azure CLI 2.0.47 or above. The following example details how you can start a rolling OS upgrade on a scale set named myScaleSet in the resource group named myResourceGroup:

az vmss rolling-upgrade start --resource-group "myResourceGroup" --name "myScaleSet" --subscription "subscriptionId"

Leverage Activity Logs for Upgrade Notifications and Insights

Activity Log is a subscription log that provides insight into subscription-level events that have occurred in Azure. Customers are able to:

• See events related to operations performed on their resources in Azure portal
• Create action groups to tune notification methods like email, sms, webhooks, or ITSM
• Set up suitable alerts using different criteria using Portal, ARM resource template, PowerShell or CLI to be sent to action groups

Customers will receive three types of notifications related to Automatic OS Upgrade operation:

• Submission of upgrade request for a particular resource
• Outcome of submission request along with any error details
• Outcome of upgrade completion along with any error details

Setting up Action Groups for Activity log alerts

An action group is a collection of notification preferences defined by the owner of an Azure subscription. Azure Monitor and Service Health alerts use action groups to notify users that an alert has been triggered.

Action groups can be created and managed using:

• ARM Resource Manager
• Portal
• PowerShell:
  • New-AzActionGroup
  • Get-AzActionGroup
  • Remove-AzActionGroup
• CLI

Customers can set up the following using action groups:

• SMS and/or Email notifications
• Webhooks - Customers can attach webhooks to their automation runbooks and configure their action groups to trigger the runbooks. You can start a runbook from a webhook
• ITSM Connections

Investigate and Resolve Auto Upgrade Errors

The platform can return errors on VMs while performing Automatic Image Upgrade with Rolling Upgrade policy. The Get Instance View of a VM contains the detailed error message to investigate and resolve an error. The Rolling Upgrades - Get Latest can provide more details on rolling upgrade configuration and status. The Get OS Upgrade History provides details on the last image upgrade operation on the scale set. Below are the topmost errors that can result in Rolling Upgrades.

RollingUpgradeInProgressWithFailedUpgradedVMs

• Error is triggered for a VM failure.
• The detailed error message mentions whether the rollout will continue/pause based on the configured threshold.

MaxUnhealthyUpgradedInstancePercentExceededInRollingUpgrade

• Error is triggered when the percent of upgraded VMs exceed the max threshold allowed for unhealthy VMs.
• The detailed error message aggregates the most common error contributing to the unhealthy VMs. See MaxUnhealthyUpgradedInstancePercent.

MaxUnhealthyInstancePercentExceededInRollingUpgrade

• Error is triggered when the percent of unhealthy VMs exceed the max threshold allowed for unhealthy VMs during an upgrade.
• The detailed error message displays the current unhealthy percent and the configured allowable unhealthy VM percentage. See maxUnhealthyInstancePercent.

MaxUnhealthyInstancePercentExceededBeforeRollingUpgrade

• Error is triggered when the percent of unhealthy VMs exceed the max threshold allowed for unhealthy VMs before an upgrade takes place.
• The detailed error message displays the current unhealthy percent and the configured allowable unhealthy VM percentage. See maxUnhealthyInstancePercent.

InternalExecutionError

• Error is triggered when an unhandled, unformatted or unexpected occurs during execution.
• The detailed error message displays the cause of the error.

RollingUpgradeTimeoutError

• Error is triggered when the rolling upgrade process has timed out.
• The detailed error message displays the length of time the system timed out after attempting to update.

Next steps