PWSH | Parallelize Invoke-VMScript - powershell

Question

I'm trying to parallelize a portion of a bigger PWSH script, basically I need to cycle through a list of VMs and execute some commands on them, and to speed up the process, I need this to be executed in parallel:
#Utils.ps1 contains all the functions
.(".\src\utils.ps1")
# List of VMs on which we execute the space reclaim
$VMs = Get-Content .\vmnames.txt
# Check if directory ./Results exists, if not it will be created
CheckDirResults
# Check if dir temp exists, if not it will be created
CheckDirTemp
# Asks for vCenter credentials
GetVServerCred
# Asks for VM credentials
GetVMCred
# Connects to vCenter
ConnectVcenter
# Commands that will be executed on VMs on line 94 (Invoke-VMScript)
$InvokeScript = #'
#! /bin/bash
pwd
'#
foreach ($vm in $VMs) {
$vms = Get-VM -Name $vm
$vms | ForEach-Object -Parallel {
Write-Output "Testing on $_"
Invoke-VMScript -VM $_ -GuestCredential $VMCred -ScriptText $InvokeScript -Confirm:$false
}
}
I also tried to simply execute the Invoke directly on $VMs like this:
$VMs | ForEach-Object -Parallel {
Write-Output "Testing on $_"
Invoke-VMScript -VM $_ -GuestCredential $VMCred -ScriptText $commands
}
In both cases, the Invoke-VMScript can't either connect to the VMs or can't find the chunk of code to execute on the VMs.
Errors:
"test.ps1" 44L, 934C 36,0-1 81%
---- ---- ----
evl6800756.sys.ntt.eu 443 VSPHERE.LOCAL\Administrator
Testing on euczdrpoc03
Testing on euczdrpoc30
Invoke-VMScript:
Line |
3 | Invoke-VMScript -VM $_ -GuestCredential $VMCred -ScriptText $comma …
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| 1/17/2023 10:42:02 AM Invoke-VMScript You are not currently connected to any servers. Please connect first using a Connect cmdlet.
Invoke-VMScript:
Line |
3 | Invoke-VMScript -VM $_ -GuestCredential $VMCred -ScriptText $comma …
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| 1/17/2023 10:42:02 AM Invoke-VMScript Value cannot be found for the mandatory parameter ScriptText
Invoke-VMScript:
Line |
3 | Invoke-VMScript -VM $_ -GuestCredential $VMCred -ScriptText $comma …
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| 1/17/2023 10:42:02 AM Invoke-VMScript You are not currently connected to any servers. Please connect first using a Connect cmdlet.
Invoke-VMScript:
Line |
3 | Invoke-VMScript -VM $_ -GuestCredential $VMCred -ScriptText $comma …
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
| 1/17/2023 10:42:02 AM Invoke-VMScript Value cannot be found for the mandatory parameter ScriptText

Answer 1

The $using: scope modifier inside a -Parallel script-block lets you refer to variables assigned a value outside that script-block. Examples in your question are not complete enough to say for certain, but hopefully this explains at least some of the difficulty.
So for example within the parallel block, try $using:commands instead of your $commands. This bit from reference doc could be more helpfully spelled out, IMHO.
Use the $using: keyword to pass variable references to the running
script.
That's demonstrated more clearly in one of the reference examples, in this blog post, and this answer.
Edit: sounds like the parallel runspaces do not inherit the vCenter connection. The open proposal for a -UseCurrentState switch to transfer the current runspace state to -Parallel loop iterations might help in your situation. Meanwhile could try passing -Server $using:DefaultVIServer to relevant commands inside the parallel block. LucD's comment that PowerCLI is not threadsafe may also be worth researching alongside the note in the reference doc:
The ForEach-Object -Parallel parameter set runs script blocks in parallel on separate process threads. The $using: keyword allows passing variable references from the cmdlet invocation thread to each running script block thread. Since the script blocks run in different threads, the object variables passed by reference must be used safely. Generally it is safe to read from referenced objects that don't change. But if the object state is being modified then you must used thread safe objects, such as .NET System.Collection.Concurrent types

Answer 2

I managed to do it this way:
# Commands that will be executed on VMs on line 94 (Invoke-VMScript)
$commands = #'
#! /bin/bash
hostname
'#
# Loads the VMs names from the file vmnames.txt
$vms = Get-Content ".\vmnames.txt"
# Uses the content of the file vmnames.txt to get the VM objects
$vmnames = Get-VM -Name $vms
# Executes the commands on the VMs
$vmnames | ForEach-Object -Parallel {
# Loads the variables in the parallel session
$commands = $using:commands
$VMCred = $using:VMCred
Invoke-VMScript -VM $_ -GuestCredential $VMCred -ScriptText $commands
}
For some reasons, piping directly $vms (so the content of the file to ForEach-Object -Parallel won't pass correctly the value (in this case the VM name), while using the Get-VM -Name $vms will do.
Then, once this is solved the ForEach-Object -Parallel will finally get the correct VM name assigned to $_.