It’s a bird, it’s a plane, it’s… Invoke-VMScript

I was at work today and a need came across my desk for a solution that requires SNMP. For some reason which I can’t fathom, SNMP is not installed as a service on the majority of the servers. Who do we turn to in tumultuous times like these? PowerShell and his mighty sidekick PowerCLI!

michael-corleone-pull-me-back-in-just-when-i-thought-i-was-out-they-pull-me-back-inFirst things first I wanted to know the scope of what I was dealing with. When I dove into this problem I had every intention of trying to broaden my horizons and move away from PowerCLI, but it’s so easy to get sucked back into what you know. Besides, I knew I was only targeting a couple of clusters, so it only made sense to go back to PowerCLI, right? Right???

If you ignore the ugly formatting, what I did below was load all of the VM’s I needed to target into an object and then iterate through each of them to make sure they were windows machines and that they were powered on. In hindsight I knew that I was probably going to use invoke-vmscript to get the job done, so I probably should have checked for vmTools status (ExtensionData.Guest.ToolsRunningStatus) while I was at it.  snmp1

So now we’ve got a nice neat little hashtable full of servers that need a little TLC. You’d think that we could immediately get rocking, but without going into details things unexpectedly got a little dodgy at this point. I mentioned earlier that I originally intended to try and break away from PowerCLI just to broaden my horizons. Unfortunately as an Infrastructure person you don’t always have the opportunity to do things the way you’d like, and you have to sacrifice elegance for just getting things done. Luckily as VMware admins when we need to get $hit done, we have a very handy and very powerful tool available to us and that is invoke-vmscript.

b436ea981cd43a8a244370d95fa3f343_super-troopers-better-fix-meow-super-troopers-meme_250-131If you’ve heard me talk, reviewed my scripts or spent any time around me you’d know that I think invoke-vmscript is the cat’s meow. It is without a doubt my favorite cmdlet as it lets you get away with some pretty awesome stuff. At it’s root, invoke-vmscript allows you to run a script via VMtools within the context of the local VM. Now this is different from PSexec or PowerShell remoting; you are actually running the a script within the local OS where VMtools and PowerCLI are just the mechanisms to enable this super hero activity.

Quick sidebar: With great power comes great responsibility. I said above that invoke-vmscript “lets you get away with some pretty awesome stuff.” Many people in this world just deploy VMtools and vCenter with default permissions and credentials. If you are a security person, you need to ensure that your roles and privileges are setup appropriately, of you could have exposure due to what you can accomplish with VMtools.

But I digress. We are here to get things done and at the center of it this whole exercise boils down to a one liner:

<strong>Invoke-VMScript -VM $client.Name -ScriptText "DISM /online /enable-feature /norestart /featurename:SNMP" -ScriptType Powershell

 

If you refer back to the original snip, we stored all of the servers into an array, which is being iterated through. We invoke the script targeting $client.name. The parameter for ScriptText is where we pass in the script that we would like to run on the remote system. In this case we are using the Microsoft DISM tool to add the SNMP feature to our Windows installation. Lastly is the parameter for ScriptType. You have three ScriptType options available to you as of today: Bat for you old school Windows Cats, Bash for the nix kittens and PowerShell for the up and coming cubs.

When you put it all together, here’s the code to get it done:

$serverset=$(get-cluster cluster1|Get-VM) + $(get-cluster cluster2|Get-VM)

$ArrRemediate=@()

foreach ($client in $serverset){

if($client.powerstate -eq "PoweredOn" -and $client.guestid.contains("windows")){

if(!$(get-service -ComputerName $client -Name SNMP -ea silentlycontinue)){
$ArrRemediate+=$client
Invoke-VMScript -VM $client.Name -ScriptText "DISM /online /enable-feature /norestart /featurename:SNMP" -ScriptType Powershell
get-service -ComputerName $client.Name -Name SNMP|Select-Object -Property name, status, starttype |ft

}

}

}

&nbsp;

$ArrRemediate.Count

I hope for today you’ll excuse the formatting and less than efficient code, as the mission was to get things done. We achieved our mission and escaped certain doom due to our friendly neigboorhood hero Invoke-VMScript. I hope to have a deeper expose into our masked super hero soon, but until then if you have any thoughts or would like to contribute to the conversation, please reach out.