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Azure – Better way to deal with multiple foreach loops in Powershell?

Is there a better way in Powershell to handle multiple levels of returned values than nested foreach loops?

I need to get a list of each of our Azure Virtual Desktop session hosts for further processing. This requires me to iterate over a list of resource groups to get the host pool(s) in each of them; iterate over those to get the session hosts within each; and finally iterate over the session hosts:

foreach ($resourceGroup in $resourceGroups) {
    $hostPoolObjects = Get-AzWvdHostPool -ResourceGroupName $resourceGroup.ResourceGroupName
        
    foreach ($hostPool in $hostPoolObjects) {
        $sessionHosts = Get-AzWvdSessionHost -ResourceGroupName $resourceGroup.ResourceGroupName -HostPoolName $hostPool.Name
        
        foreach ($sessionHost in $sessionHosts) {
            # Further processing
        }
    }
}

That seems inefficient. and, knowing how many session hosts I’m dealing with, memory intensive. Is there another method I could be using? I’m looking into whether multithreading would help in any way; maybe for the foreach ($hostPool in $hostPoolObjects) block.

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2

Answers


  1. 0

    There is a way you can reduce 1 of the loops by using a Resource Graph query (Search-AzGraph). This example gets all Host Pools with their corresponding Resource Group and Subscription:

    $searchAzGraphSplat = @{
    Query = "
        resources
        | where ['type'] == 'microsoft.desktopvirtualization/hostpools
        | project name, resourceGroup, subscriptionId"
}

$allHostPools = do {
    $response = Search-AzGraph @searchAzGraphSplat
    $searchAzGraphSplat['SkipToken'] = $response.SkipToken
    if ($response.Data.Count) {
        $response.Data
    }
}
while ($response.SkipToken)

foreach ($hostpool in $allHostPools) {
    $getAzWvdSessionHostSplat = @{
        ResourceGroupName = $hostpool.resourceGroup
        HostPoolName      = $hostPool.name
    }

    foreach ($sessionHost in Get-AzWvdSessionHost @getAzWvdSessionHostSplat) {
        # Further processing
    }
}

    From there if you need faster processing you could use ForEach-Object -Parallel instead but you need PowerShell 7+ for that:

    $allHostPools | ForEach-Object -Parallel {
    $getAzWvdSessionHostSplat = @{
        ResourceGroupName = $_.resourceGroup
        HostPoolName      = $_.name
    }

    foreach ($sessionHost in Get-AzWvdSessionHost @getAzWvdSessionHostSplat) {
        # Further processing
    }
}

    If you’re stuck with Windows PowerShell you can have a look at this Q&A and this module.

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  2. 0

    Fundamentally, you can take advantage of the PowerShell pipeline‘s auto-enumeration behavior and the ability of most cmdlets to accept object-by-object input via the pipeline:

    $resourceGroups | ForEach-Object {
  Get-AzWvdHostPool -ResourceGroupName $resourceGroup.ResourceGroupName |
    Get-AzWvdSessionHost | ForEach-Object {      
      $sessionHost = $_ 
      # Further processing...
    }
}

    Note:

    • The above invariably performs sequential object-by-object processing.

    • In PowerShell (Core) 7, you can speed up processing with parallel processing, using the ForEach-Object cmdlet’s -Parallel parameter; as noted in Santiago’s answer, alternative solutions are available in Windows PowerShell (the legacy, ships-with-Windows, Windows-only edition of PowerShell whose latest and last version is 5.1).

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