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Deploy A Windows VMSS with MSI

This template shows how to use Managed Service Idenity with VM Scale Sets and how to access azure resources from within VMs in the Scale Set, in particular it shows how to:

  • Create a VM SCale Set with a system assigned idenity
  • Install the MSI extension to allow OAuth tokens to be issued for Azure resources
  • Assign RBAC permissions to the Managed Identity
  • Run a script that uses Azure PowerShell modules with the MSI

This template creates a new Windows VM Scale Set with a MSI and deploys the MSI extension to each VM. The MSI associated with the VM Scale Set is given owner permission on a storage account that is created by the template. A PowerShell script is then run on each VM in the Scale Set using the customscript extension , this script installs Azure Powershell Modules and logs in using an OAuth token returned from the token issuing endpoint provided by the MSI extension. It then uses the Azure PowerShell modules to retrieve the keys for the storage account and writes a blob with a name matching the VM name into the storage account.

The script depends on PowerShell 5.0 or above as it uses PowerShell Package Management to install the Azure AD modules, it therefore requires either Windows Server 2016, or if not using Windows Server 2016 for WMF5 or above to be installed on the VM or for the Package Managment Modules targeted for PowerShell 3 or 4 to be installed. Alternatively the script could be updated to install Azure PowerShell using a different mechamism.

In order to make sure that the MSI is created and given permissions before the scripts run first the VM Scale Set is created with 0 instances, the MSI is then given RBAC permissions and then the VS Scale Set is updated to create the VMs with the extensions.

The default configuration will deploy a scaleset with 2 DS1_V2 VMs.