How to reboot VMs in a VMSS after an ARM Template Custom Script Extension is ran?

hi jerred! great question ))

first, u can actually add a simple reboot command right inside ur custom script extension. just slap a 'restart computer' at the end if u're using powershell. like this

Restart-Computer -Force 

but hey, if u need a delay (like ur 10-minute idea), u can totally schedule it. this works inside the script too ))

Register-ScheduledTask -Action (New-ScheduledTaskAction -Execute 'shutdown.exe' -Argument '/r /f') -Trigger (New-ScheduledTaskTrigger -Once -At (Get-Date).AddMinutes(10)) -TaskName 'DelayedReboot'  

or, if u prefer the azure way, u can trigger a rolling reboot after the extension finishes. https://docs.microsoft.com/en-us/azure/virtual-machine-scale-sets/virtual-machine-scale-sets-manage-cli#reboot-vms-in-a-scale-set

just run az vmss restart --resource-group myResourceGroup --name myScaleSet --instance-ids *

also, if u're dealing with http service changes, maybe just restarting that service could save u time? worth looking into ))

Restart-Service -Name 'HTTP' -Force 

as well check this https://docs.microsoft.com/en-us/azure/virtual-machines/extensions/custom-script-windows for more on custom script tweaks.

this scheduling trick might help in other tools too. u never know when u'll need a delayed restart ))

hope this sorts it out for u! let us know if u hit any snags...

Best regards,

Alex

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P.S. If my answer help to you, please Accept my answer

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Hi Jerred Moss,

You're correct to be cautious, and your interpretation of the Microsoft documentation is spot on. As per documents:

"Don't put restarts inside the script.": refers to direct calls like Restart-Computer, shutdown.exe, or Restart-Service. The Custom Script Extension (CSE) doesn’t wait for the VM to come back up — it marks the operation as failed or stuck. Rebooting in the middle of script execution may interrupt other extensions (e.g., monitoring agents, antivirus, DSC, etc.) that are still installing.

Schedule the restart by using a Windows Scheduled Task..." the recommended, supported pattern to defer restarts or service reloads until after CSE has exited cleanly. It guarantees that Azure marks the extension as Provisioning succeeded, preventing the VM or VMSS instance from being flagged as unhealthy.

"Don't stop or update the VM agent." The Azure VM agent manages extensions. If it’s killed or updated unexpectedly by your script, it can leave the VM in a broken provisioning state.

At the very end of your script, add a Windows Scheduled Task that delays a reboot or restarts the service — after CSE is long gone.

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