Hardening PowerShell Script for Automating Usage of VMs using PowerCLI

Question

To get a clean environment to run some other scripts I need to revert a Virtual Machine on an ESX Host every time when a Scheduled Task triggers it.

Reverting can be achieved by running:

Set-VM -VM $VMName -Snapshot "MySnapshot" -Confirm:$false

Starting can be achieved by running:

Start-VM -VM $VMName

Stopping can be achieved by running:

Shutdown-VMGuest -VM $VMName -Confirm:$false

How can I handle this in a more secure way, e.g to be able to handle Errors when reverting, starting or stopping the VM and get a return if one of these Tasks were being executed successfully?

I am using PowerCLI 6.5.0.

Answer 1

You can use several methods to achieve this. Here are 2 examples :

1. Using -ErrorVariable

   # Revert VM
   Set-VM -VM $VMName -Snapshot "MySnapshot" -Confirm:$false -ErrorVariable revertError
   
   If ($revertError)
   {
       Write-Host "An error occured while reverting snapshot !" -ForegroundColor Red
       Write-Host $revertError
   }
   Else
   {
       Write-Host "Successfully reverted to snapshot." -ForegroundColor Green
   }
   
   # Start VM
   Start-VM -VM $VMName -ErrorVariable startError
   
   If ($startError)
   {
       Write-Host "An error occured while starting VM :" -ForegroundColor Red
       Write-Host $startError
   }
   Else
   {
       Write-Host "Successfully started VM." -ForegroundColor Green
   }
   
   # Stop VM
   Shutdown-VMGuest -VM $VMName -Confirm:$false -ErrorVariable shutdownError
   
   If ($shutdownError)
   {
       Write-Host "An error occured while shutting down guest OS of VM :" -ForegroundColor Red
       Write-Host $shutdownError
   }
   Else
   {
       Write-Host "Successfully stopped VM." -ForegroundColor Green
   }
   

2. Using Try/Catch as mentionned by @mark-wragg

   # Revert VM
   Try
   {
       # Temporarily make all errors terminating
       $errorActionPreference = "Stop"
       Set-VM -VM $VMName -Snapshot "MySnapshot" -Confirm:$false
       Write-Host "Successfully reverted to snapshot." -ForegroundColor Green
   }
   Catch
   {
       Write-Host "An error occured while reverting snapshot !" -ForegroundColor Red
       Write-Host $_.Exception.Message
   }
   Finally
   {
       $errorActionPreference = "Continue"
   }
   
   # Start VM
   Try
   {
       # Temporarily make all errors terminating
       $errorActionPreference = "Stop"
       Start-VM -VM $VMName
       Write-Host "Successfully started VM." -ForegroundColor Green
   }
   Catch
   {
       Write-Host "An error occured while starting VM :" -ForegroundColor Red
       Write-Host $_.Exception.Message
   }
   Finally
   {
       $errorActionPreference = "Continue"
   }
   
   # Stop VM
   Try
   {
       # Temporarily make all errors terminating
       $errorActionPreference = "Stop"
       Shutdown-VMGuest -VM $VMName -Confirm:$false
       Write-Host "Successfully stopped VM." -ForegroundColor Green
   }
   Catch
   {
       Write-Host "An error occured while shutting down guest OS of VM :" -ForegroundColor Red
       Write-Host $_.Exception.Message
   }
   Finally
   {
       $errorActionPreference = "Continue"
   }