Start and Stop Azure VM’s (and more) in Parallel from Powershell

Edit 2017: With the change to AzureRM this approach need some tweaking, see this new GIST for how to allow AzureRM to execute commands in Powershell jobs. The script itself is used to remove deployment history for a resource group but can easily be edited to work on VMs.

So I’ve got a demo that I’ve put together that uses a LOAD of Azure VM’s to demonstrate scripting against them.

To make sure I don’t get charged for them while I’m not using them I’ve got the following powershell to start and stop them:

Get-AzureVM | Stop-AzureVM –Force

Get-AzureVM | Start-AzureVM

I notice that this took a longer than I was expecting and so I started to do some digging. It turn out the PowerShell pipeline is executing these API requests in a synchronous way. Firing off the first request, waiting for the response and then, when completed, moving on to the next. This wouldn’t be a problem if I didn’t have loads of VM’s!

So I wrote the following, it uses PowerShell Jobs (think Task<T> if you’re a C# person), to kick these off as background jobs that run in parallel. (nb. You have to pass the variables in as arguments to the script block)

	$vms = Get-azurevm \| ?{ $_.Status -eq "StoppedDeallocated"}
	$jobs = @()
	foreach ($vm in $vms)
	{
	$params = @($vm.Name, $vm.ServiceName)
	$job = Start-Job -ScriptBlock {
	param($ComputerName, $ServiceName)
	start-Azurevm -Name $ComputerName -ServiceName $ServiceName
	} -ArgumentList $params
	$jobs = $jobs + $job
	}

	# Wait for it all to complete
	Wait-Job -Job $jobs

	# Getting the information back from the jobs
	Get-Job \| Receive-Job

view raw gistfile1.ps1 hosted with ❤ by GitHub

Now we get this lovely output. These all run as individual jobs and complete asynchronously, we then wait for all of them (think WaitAll() for C#). Now I can start all of my machines in the demo really quickly!

This is really useful in other scenarios too, think of any time you’re waiting on azure management API and the actions could be done simultaneously.

Id Name PSJobTypeName State HasMoreData Location Command

— —- ————- —– ———– ——– ——-

22 Job22 BackgroundJob Running True localhost …

24 Job24 BackgroundJob Running True localhost …

26 Job26 BackgroundJob Running True localhost …

28 Job28 BackgroundJob Running True localhost …

30 Job30 BackgroundJob Running True localhost …

RunspaceId : 88465362-c8ce-45de-866d-9ced85cc3e40