Start-Job like a boss

Ever wanted to Start Background Jobs (Start-Job) with some Throttle? Or with a Timeout? And how about loading your local user session functions inside your Background Job?

I use Start-Job daily. Managing +300 VMs for our QA environment in VCenter (VMWare) and SCVMM (Hyper-V). It’s a breeze when you know how to do things in parallel. Many scripts/modules are out there to help you do it quickly and efficiently. Most of them, are built around Runspaces and for good reasons. Using Runspaces are blazing fast! But in some cases, using Runspaces isn’t the right option. For those times, I’ve built Invoke-Job.

I wanted to replicate the Start-Job cmdlet, but add a few extra parameters:

• ImportFunctions
• Throttle
• Timeout
• PassThru

Link: https://github.com/mkellerman/Invoke-Job

Let’s make a simple example:

Import-Module .\Invoke-Job.ps1

function Invoke-HelloWorld { 
    Write-Warning 'Hello World'
}

(1..10) | Invoke-Job -ScriptBlock { Invoke-HelloWorld } -ImportFunctions -Throttle 3 -All

This example shows how to invoke a custom function, inside of the background job, without having to do anything to load that function. It does it all for me. the -All parameter will show be jobs when they are starting and when they are completed. If you remove that parameter, you’ll only see when they are done. As a DevOps, i like seeing things start/stop. ;)

Now that we get the basics, let’s bump it up a notch:

Import-Module .\Invoke-Job.ps1

# Load a script in this user session
# https://gallery.technet.microsoft.com/scriptcenter/Get-PendingReboot-Query-bdb79542
Import-Module .\Get-PendingReboot.ps1

# Make a simple ScriptBlock that will receive the computername from the pipeline and execute the script against the remote computer. In this case, Get-PendingReboot that we've loaded in this current session.

$ScriptBlock = {
  Process {
    
    # Collect the InputObject sent through the Pipeline.
    $ComputerName = $_
    
    Try   { 
    
      # Because Get-PendingReboot has been imported into this session, I can call the function directly.
      # I'm also $Using variables from the parent session. Everything works as expected.
      
      Invoke-Command -ComputerName $ComputerName -Credential $Using:Credential -ScriptBlock ${function:Get-PendingReboot} 
    
    } Catch { 
    
      Write-Error $_.Exception.Message 
    
    }
  
  }
}

# Get list of computers and set the credential used for the remote execution.

$Computers = Get-Content -Path '.\computers.txt'
$Credential = Get-Credential

# Start-Job 4 jobs at a time, with a timeout of 30 seconds, and return the results (not the Job object). And beautify it by presenting the results in a table.

$Computers | Invoke-Job -ScriptBlock $ScriptBlock -Throttle 4 -Timeout 30 -ImportFunctions -PassThru | Format-Table

This example shows how to execute a function against many computers, but with a throttle and a timeout. And output the results directly.

And here you go. Simple and easy to read code. If I had to put the code here to handle the Throttle, the Timeout, ImportFunctions and the PassThru, it would have been +250 lines of code and hard for someone else to read and maintain.

Let me know what you guys think!

Msg me on Twitter, love getting your feedback!

Link: https://github.com/mkellerman/Invoke-Job