Can I have an ARM template resource with a COPY array of 0 to N

Question

I'm deploying an ARM template that uses a copy resource block to deploy 1 or more data disks to a VM. What I'd like to do is change this to 0 or more.

The parameter I use is

    "VirtualMachineDiskSizeArray": {
        "type": "array",
        "defaultValue": [ "100" ]
    },

Which is then called in a resource:

   "resources": [
    {
        "name": "[parameters('virtualMachineName')]",
        "type": "Microsoft.Compute/virtualMachines",
        "apiVersion": "2016-04-30-preview",
        "location": "[parameters('rgLocation')]",
        "dependsOn": [
            "[concat('Microsoft.Storage/storageAccounts/', parameters('rgStorageAccountName'))]"
        ],
        "properties": {
            "osProfile": { ... },
            "hardwareProfile": { ... },
            "storageProfile": {
                "imageReference": { ... },
                "osDisk": { ... },
                "copy": [
                    {
                        "name": "dataDisks",
                        "count": "[length(parameters('VirtualMachineDiskSizeArray'))]",
                        "input": {
                            "lun": "[copyIndex('dataDisks')]",
                            "name": "[concat(parameters('vmDataDiskNameStub'), add(copyIndex('dataDisks'),1), '.vhd')]",
                            "diskSizeGB": "[parameters('VirtualMachineDiskSizeArray')[copyIndex('dataDisks')]]",
                            "createOption": "Empty",
                            "vhd": {
                                "uri": "[concat(concat(reference(resourceId(parameters('rgName'), 'Microsoft.Storage/storageAccounts', parameters('rgStorageAccountName')), '2015-06-15').primaryEndpoints['blob'], 'vhds/'), concat(parameters('vmDataDiskNameStub'),  add(copyIndex('dataDisks'),1), '.vhd') )]"
                            }
                        }
                    }
                ]
            }
        }
    },

However, when I pass in an array of data disks with 0 elements, I get this error, as expected:

Validation returned the following errors:
: Deployment template validation failed: 'The template 'copy' definition at line '0' and column '0' has an invalid copy count. The co
py count must be a postive integer value and cannot exceed '800'. Please see https://aka.ms/arm-copy for usage details.'.

Template is invalid.

I would like to try to work around this somehow - I tried adding a condition on the copy:

"condition": "[  greater(length(parameters('VirtualMachineDiskSizeArray')), 0)]",

But that returned the same error.

I'm researching nested templates, but that doesn't look good for a section of a resource.

Answer 1

The easiest way to work around that is using this:

{
    "condition": "[if(equals(parameters('numberOfDataDisks'), 0), bool('false'), bool('true'))]",
    "apiVersion": "2017-03-30",
    "type": "Microsoft.Compute/virtualMachines",
    "name": "[variables('vmName')]",
    "location": "[resourceGroup().location]",
    "properties": {
        "storageProfile": {
            "imageReference": { xxx },
            "osDisk": { xxx },
            "copy": [
                {
                    "name": "dataDisks",
                    "count": "[if(equals(parameters('numberOfDataDisks'), 0), 1, parameters('numberOfDataDisks'))]",
                    "input": {
                        "diskSizeGB": "1023",
                        "lun": "[copyIndex('dataDisks')]",
                        "createOption": "Empty"
                    }
                }
            ]
        }
    }
}

this will work around the fact that you are passing 0 data disks and at the same time wont deploy this vm. all you need to do is add another vm resource. But it has to be with a different name (else template will fail) or you can use nested template to deploy a vm with the same name.

this can be improved with recent fixes to if() function, you can always work around by using nested deployments as well