Azure VM Custom script extension identity access to Storage Account - azure

Question

In the custom script extension of a VM I want to execute this command:
#download azcopy from http://aka.ms/downloadazcopy
c:\azcopy login --identity
C:\azcopy copy https://mystorage.blob.core.windows.net/software C:\Temp --recursive
But for this to work the identity of the VM need to be added as "Storage Blob Data Contributor". In terraform we could do it this way
resource"azurerm_role_assignment""role" {​​​​​​​​
scope= data.azurerm_storage_account.vault.id
role_definition_name="Storage Blob Data Contributor"
principal_id= azurerm_windows_virtual_machine.vm.identity.0.principal_id
}​​​​​​​​
But if we do not use terraform and instead use Azure DevOps and ARM templates, how would you execute it ? Because the VM is not created yet to give identity access. Custom script extension is part of the creation.

Answer 1

You can enable a system-assigned managed identity using an Azure Resource Manager template. Reference here.
Step1
To enable system-assigned managed identity, locate the Microsoft.Compute/virtualMachines resource of interest within the resources section and add the "identity" property at the same level as the "type": "Microsoft.Compute/virtualMachines" property. Use the following syntax:
"identity": {
"type": "SystemAssigned"
},
Step2
When you're done, the following sections should be added to the resource section of your template and it should resemble the following:
"resources": [
{
//other resource provider properties...
"apiVersion": "2018-06-01",
"type": "Microsoft.Compute/virtualMachines",
"name": "[variables('vmName')]",
"location": "[resourceGroup().location]",
"identity": {
"type": "SystemAssigned",
},
},
//The following appears only if you provisioned the optional VM extension (to be deprecated)
{
"type": "Microsoft.Compute/virtualMachines/extensions",
"name": "[concat(variables('vmName'),'/ManagedIdentityExtensionForWindows')]",
"apiVersion": "2018-06-01",
"location": "[resourceGroup().location]",
"dependsOn": [
"[concat('Microsoft.Compute/virtualMachines/', variables('vmName'))]"
],
"properties": {
"publisher": "Microsoft.ManagedIdentity",
"type": "ManagedIdentityExtensionForWindows",
"typeHandlerVersion": "1.0",
"autoUpgradeMinorVersion": true,
"settings": {
"port": 50342
}
}
}
]
Step3
Grant it a role "Storage Blob Data Contributor" access to the resource group in which it was created.
Under the parameters section add the following:
"builtInRoleType": {
"type": "string",
"defaultValue": "StorageBlobDataContributor"
},
"rbacGuid": {
"type": "string"
}
Under the variables section add the following:
"StorageBlobDataContributor": "[concat('/subscriptions/', subscription().subscriptionId, '/providers/Microsoft.Authorization/roleDefinitions/', 'ba92f5b4-2d11-453d-a403-e96b0029c9fe')]"
Under the resources section add the following:
{
"apiVersion": "2017-09-01",
"type": "Microsoft.Authorization/roleAssignments",
"name": "[parameters('rbacGuid')]",
"properties": {
"roleDefinitionId": "[variables(parameters('builtInRoleType'))]",
"principalId": "[reference(variables('vmResourceId'), '2017-12-01', 'Full').identity.principalId]",
"scope": "[resourceGroup().id]"
},
"dependsOn": [
"[concat('Microsoft.Compute/virtualMachines/', parameters('vmName'))]"
]
}
Update
To grant the identity with an RBAC role to access a specific storage account. Refer to this answer.
{
"apiVersion": "2018-01-01-preview",
"type": "Microsoft.Storage/storageAccounts/providers/roleAssignments",
"name": "[concat(variables('storageAccountName'), '/Microsoft.Authorization/',parameters('rbacGuid'))]",
"properties": {
"roleDefinitionId": "[variables(parameters('builtInRoleType'))]",
"principalId": "[reference(resourceId('Microsoft.Compute/virtualMachines',parameters('vmName')), '2017-12-01', 'Full').identity.principalId]"
},
"dependsOn": [
"[concat('Microsoft.Compute/virtualMachines/', parameters('vmName'))]"
]
}