Tag: Azure Monitor

Below is a sample script for adding Azure Metrics alerts using Azure Monitor. It is possible to create alerts using the Azure Portal, but that doesn’t scale well because each alert is specific to one VM. For example, if you have 4 alerts per VM, and 10 VMs, then you have to create 40 alerts! One could say: Use Log Analytics, but there’s a cost to that, and I find the OMS Workspace to be immature. Instead, one can continue to use Resource/Azure Monitor metrics, but script the creation of the metrics alerts.

Once could use JSON, but again, there’s a scale-out issue there unless you build this into every deployment. But the advantage with PowerShell is that you can automatically vary thresholds based on the VM’s spec, as you will see below – some metric thresholds vary depending on the spec of a machine, e.g. the number of cores.

The magic cmdlet for doing this work is Add-AzureRmMetricAlertRule. And the key to making that cmdlet work is to know the name of the metric. Microsoft’s docs state that you can query for available metrics using Get-AzureRmMetricDefinition, but I found that with VMs, it only returned back the Host metrics and not the Guest metrics. I had to do some experimenting, but I found that the names of the guest metrics are predictable; they’re exactly what you see in the Azure Portal, e.g. \System\Processor Queue Length.

The below script is made up of a start and 2 functions:

1. The start is where I specify some variables to define the VM, resource group name, and query for the location of the VM. The start can then call a series of functions, one for each metric type. In this example, I call ProcessorQLength.
2. The ProcessorQLength function takes the VM, queries for it’s size, and then gets the number of cores assigned to that VM. We need that because the alert should be triggers if the average queue length per core is over 4, e.g. 12 for a 4 core VM. The AddMetric function is called with a configuration for the \System\Processor Queue Length alert.
3. The AddMetric function is a generic function capable of creating any Azure metrics alert. It is configured by the parameters that are fed into it, in this case by the ProcessorQLength function.

Here’s my example:

#A generic function to create an Azure Metrics alert
function AddMetric ($FunMetricName, $FuncMetric, $FuncCondition, $FuncThreshold, $FuncWindowSize, $FuncTimeOperator, $FuncDescription)
{
    $VMID = (Get-AzureRmVM -ResourceGroupName $RGName -Name $VMName).Id
    Add-AzureRmMetricAlertRule -Name $FunMetricName -Location $VMLocation -ResourceGroup $RGName -TargetResourceId $VMID -MetricName $FuncMetric -Operator $FuncCondition -Threshold $FuncThreshold -WindowSize $FuncWindowSize -TimeAggregationOperator $FuncTimeOperator -Description $FuncDescription
}

#Create an alert for Processor Queue Length being 4x the number of cores in a VM
function ProcessorQLength ()
{
    $VMSize = (Get-AzureRMVM -ResourceGroupName $RGName -Name $VMName).HardwareProfile.VmSize
    $Cores = (Get-AzureRMVMSize -Location $VMLocation | Where-Object {$_.Name -eq $VMSize}).NumberOfCores
    $QThreshold = $Cores * 4
    AddMetric "$VMname - CPU Q Length" "\System\Processor Queue Length" "GreaterThan" $QThreshold "00:05:00" "Average" "Created using PowerShell"
}

#The script starts here
#Specify a VM name/resource group
$VMName = "vm-test-01"
$RGName = "test"
$VMLocation = (Get-AzureRMVM -ResourceGroupName $RGName -Name $VMName).Location

#Start running functions to create alerts
ProcessorQLength

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