Azure Monitor autoscaling common metrics

Article
03/09/2023
5 minutes to read

Note

We recommend that you use the Azure Az PowerShell module to interact with Azure. See Install Azure PowerShell to get started. To learn how to migrate to the Az PowerShell module, see Migrate Azure PowerShell from AzureRM to Az.

Azure Monitor autoscaling allows you to scale the number of running instances up or down, based on telemetry data, also known as metrics. This article describes common metrics that you might want to use. In the Azure portal, you can choose the metric of the resource to scale by. You can also choose any metric from a different resource to scale by.

Azure Monitor autoscale applies only to Azure Virtual Machine Scale Sets, Azure Cloud Services, Azure App Service - Web Apps, and Azure API Management. Other Azure services use different scaling methods.

Compute metrics for Resource Manager-based VMs

By default, Azure Resource Manager-based virtual machines and virtual machine scale sets emit basic (host-level) metrics. In addition, when you configure diagnostics data collection for an Azure VM and virtual machine scale sets, the Azure Diagnostics extension also emits guest-OS performance counters. These counters are commonly known as "guest-OS metrics." You use all these metrics in autoscale rules.

You can use the Get MetricDefinitions API/PoSH/CLI to view the metrics available for your Virtual Machine Scale Sets resource.

If you're using virtual machine scale sets and you don't see a particular metric listed, it's likely disabled in your Diagnostics extension.

If a particular metric isn't being sampled or transferred at the frequency you want, you can update the diagnostics configuration.

If either preceding case is true, see Use PowerShell to enable Azure Diagnostics in a virtual machine running Windows to configure and update your Azure VM Diagnostics extension to enable the metric. The article also includes a sample diagnostics configuration file.

Host metrics for Resource Manager-based Windows and Linux VMs

The following host-level metrics are emitted by default for Azure VM and virtual machine scale sets in both Windows and Linux instances. These metrics describe your Azure VM but are collected from the Azure VM host rather than via agent installed on the guest VM. You can use these metrics in autoscaling rules.

Guest OS metrics for Resource Manager-based Windows VMs

When you create a VM in Azure, diagnostics is enabled by using the Diagnostics extension. The Diagnostics extension emits a set of metrics taken from inside of the VM. This means you can autoscale off of metrics that aren't emitted by default.

You can generate a list of the metrics by using the following command in PowerShell.

Get-AzMetricDefinition -ResourceId <resource_id> | Format-Table -Property Name,Unit

You can create an alert for the following metrics:

Metric name	Unit
\Processor(_Total)% Processor Time	Percent
\Processor(_Total)% Privileged Time	Percent
\Processor(_Total)% User Time	Percent
\Processor Information(_Total)\Processor Frequency	Count
\System\Processes	Count
\Process(_Total)\Thread Count	Count
\Process(_Total)\Handle Count	Count
\Memory% Committed Bytes In Use	Percent
\Memory\Available Bytes	Bytes
\Memory\Committed Bytes	Bytes
\Memory\Commit Limit	Bytes
\Memory\Pool Paged Bytes	Bytes
\Memory\Pool Nonpaged Bytes	Bytes
\PhysicalDisk(_Total)% Disk Time	Percent
\PhysicalDisk(_Total)% Disk Read Time	Percent
\PhysicalDisk(_Total)% Disk Write Time	Percent
\PhysicalDisk(_Total)\Disk Transfers/sec	CountPerSecond
\PhysicalDisk(_Total)\Disk Reads/sec	CountPerSecond
\PhysicalDisk(_Total)\Disk Writes/sec	CountPerSecond
\PhysicalDisk(_Total)\Disk Bytes/sec	BytesPerSecond
\PhysicalDisk(_Total)\Disk Read Bytes/sec	BytesPerSecond
\PhysicalDisk(_Total)\Disk Write Bytes/sec	BytesPerSecond
\PhysicalDisk(_Total)\Avg. Disk Queue Length	Count
\PhysicalDisk(_Total)\Avg. Disk Read Queue Length	Count
\PhysicalDisk(_Total)\Avg. Disk Write Queue Length	Count
\LogicalDisk(_Total)% Free Space	Percent
\LogicalDisk(_Total)\Free Megabytes	Count

Guest OS metrics Linux VMs

When you create a VM in Azure, diagnostics is enabled by default by using the Diagnostics extension.

You can generate a list of the metrics by using the following command in PowerShell.

Get-AzMetricDefinition -ResourceId <resource_id> | Format-Table -Property Name,Unit

You can create an alert for the following metrics:

Metric name	Unit
\Memory\AvailableMemory	Bytes
\Memory\PercentAvailableMemory	Percent
\Memory\UsedMemory	Bytes
\Memory\PercentUsedMemory	Percent
\Memory\PercentUsedByCache	Percent
\Memory\PagesPerSec	CountPerSecond
\Memory\PagesReadPerSec	CountPerSecond
\Memory\PagesWrittenPerSec	CountPerSecond
\Memory\AvailableSwap	Bytes
\Memory\PercentAvailableSwap	Percent
\Memory\UsedSwap	Bytes
\Memory\PercentUsedSwap	Percent
\Processor\PercentIdleTime	Percent
\Processor\PercentUserTime	Percent
\Processor\PercentNiceTime	Percent
\Processor\PercentPrivilegedTime	Percent
\Processor\PercentInterruptTime	Percent
\Processor\PercentDPCTime	Percent
\Processor\PercentProcessorTime	Percent
\Processor\PercentIOWaitTime	Percent
\PhysicalDisk\BytesPerSecond	BytesPerSecond
\PhysicalDisk\ReadBytesPerSecond	BytesPerSecond
\PhysicalDisk\WriteBytesPerSecond	BytesPerSecond
\PhysicalDisk\TransfersPerSecond	CountPerSecond
\PhysicalDisk\ReadsPerSecond	CountPerSecond
\PhysicalDisk\WritesPerSecond	CountPerSecond
\PhysicalDisk\AverageReadTime	Seconds
\PhysicalDisk\AverageWriteTime	Seconds
\PhysicalDisk\AverageTransferTime	Seconds
\PhysicalDisk\AverageDiskQueueLength	Count
\NetworkInterface\BytesTransmitted	Bytes
\NetworkInterface\BytesReceived	Bytes
\NetworkInterface\PacketsTransmitted	Count
\NetworkInterface\PacketsReceived	Count
\NetworkInterface\BytesTotal	Bytes
\NetworkInterface\TotalRxErrors	Count
\NetworkInterface\TotalTxErrors	Count
\NetworkInterface\TotalCollisions	Count

Commonly used App Service (server farm) metrics

You can also perform autoscale based on common web server metrics such as the HTTP queue length. Its metric name is HttpQueueLength. The following section lists available server farm (App Service) metrics.

Web Apps metrics

You can generate a list of the Web Apps metrics by using the following command in PowerShell:

Get-AzMetricDefinition -ResourceId <resource_id> | Format-Table -Property Name,Unit

You can alert on or scale by these metrics.

Metric name	Unit
CpuPercentage	Percent
MemoryPercentage	Percent
DiskQueueLength	Count
HttpQueueLength	Count
BytesReceived	Bytes
BytesSent	Bytes

Commonly used Storage metrics

You can scale by Azure Storage queue length, which is the number of messages in the Storage queue. Storage queue length is a special metric, and the threshold is the number of messages per instance. For example, if there are two instances and if the threshold is set to 100, scaling occurs when the total number of messages in the queue is 200. That amount can be 100 messages per instance, 120 plus 80, or any other combination that adds up to 200 or more.

Configure this setting in the Azure portal in the Settings pane. For virtual machine scale sets, you can update the autoscale setting in the Resource Manager template to use metricName as ApproximateMessageCount and pass the ID of the storage queue as metricResourceUri.

For example, with a Classic Storage account, the autoscale setting metricTrigger would include:

"metricName": "ApproximateMessageCount",
"metricNamespace": "",
"metricResourceUri": "/subscriptions/SUBSCRIPTION_ID/resourceGroups/RES_GROUP_NAME/providers/Microsoft.ClassicStorage/storageAccounts/STORAGE_ACCOUNT_NAME/services/queue/queues/QUEUE_NAME"

For a (non-classic) Storage account, the metricTrigger setting would include:

"metricName": "ApproximateMessageCount",
"metricNamespace": "",
"metricResourceUri": "/subscriptions/SUBSCRIPTION_ID/resourceGroups/RES_GROUP_NAME/providers/Microsoft.Storage/storageAccounts/STORAGE_ACCOUNT_NAME/services/queue/queues/QUEUE_NAME"

Commonly used Service Bus metrics

You can scale by Azure Service Bus queue length, which is the number of messages in the Service Bus queue. Service Bus queue length is a special metric, and the threshold is the number of messages per instance. For example, if there are two instances and if the threshold is set to 100, scaling occurs when the total number of messages in the queue is 200. That amount can be 100 messages per instance, 120 plus 80, or any other combination that adds up to 200 or more.

For virtual machine scale sets, you can update the autoscale setting in the Resource Manager template to use metricName as ApproximateMessageCount and pass the ID of the storage queue as metricResourceUri.

"metricName": "ApproximateMessageCount",
 "metricNamespace": "",
"metricResourceUri": "/subscriptions/SUBSCRIPTION_ID/resourceGroups/RES_GROUP_NAME/providers/Microsoft.ServiceBus/namespaces/SB_NAMESPACE/queues/QUEUE_NAME"