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

Answer 2

I'm going to use this answer to use a reference on my research into nested templates.

Looking at here I can see an approach that would have two nested templates, one like this:

"resources": [
{
    "name": "MultiDataDisk",
    "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') )]"
                        }
                    }
                }
            ]
        }
    }
}
]

and one like this:

"resources": [
{
    "name": "ZeroDataDisk",
    "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": { ... },
             "dataDisks": []
        }
    }
}
] 

And reference them from a parent template:

"parameters": {
 "nestedType": {
  "type": "string",
  "defaultValue": "ZeroDataDisk",
  "allowedValues": [
   "ZeroDataDisk",
   "MultiDataDisk"
  ],
 }
},
"resources": [
 {
 "name": "[concat("nested-",parameters('virtualMachineName')]",
 "type": "Microsoft.Resources/deployments",
 "apiVersion": "2015-01-01",
 "properties": {
  "mode": "Incremental",
  "templateLink": {
   "uri": "[concat('https://someplace.on.the.internet/nested/',parameter('nestedType'),".json")],
   "contentVersion": "1.0.0.0"
   },
   "parameters": {
    "rgStorageAccountName": {
     "value": "[parameters(rgStorageAccountName)]"
    },
    "OtherParms": {
     "value": "[parameters('otherParms')]"
    }
     . . .
  }
 }
]
}

However, I don't believe this is better/easier than what I did in my "Interest of Time" answer because

1. The section that I'm interested in (dataDisks) is surrounded by a bunch of other json that doesn't change leaving me to the same crappy issue of having to manually sync code between two files.
2. I now have to not only maintain two json files for the nested resources, but I have to publish them via a publicly accessible URL.

So basically, unless I can have a copy of 0-N of a section (rather than 1-N) or nest just a section, my two file hack with the powershell switch seems to be the least overhead.

Answer 3

I would like to share our solution based many of the answers already here. This is a simple example to have an input array of disks - values being their sizes - and create with those with your vm. works from 0-n. n needs to be smaller than supported disks of your VM size and other azure limits :) This should also help with this comment

{
    "$schema": "http://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#",
    "contentVersion": "1.0.0.0",
    "parameters": {
        [...]
        "dataDiskArray": {
            "type": "array",
            "defaultValue": [
                "100",
                "50"
            ]
        }
    },
    "variables": {
        "copy": [
            {
                "name": "dataDisks",
                "count": "[if(equals(length(parameters('dataDiskArray')),0),1, length(parameters('dataDiskArray')))]",
                "input": {
                    "lun": "[if(equals(length(parameters('dataDiskArray')),0),0, copyIndex('dataDisks'))]",
                    "createOption": "Empty",
                    "diskSizeGB": "[if(equals(length(parameters('dataDiskArray')),0),10,parameters('dataDiskArray')[copyIndex('dataDisks')])]"
                }
            }
        ]
    },
    "resources": [
        {
            "name": "[parameters('virtualMachineName')]",
            "type": "Microsoft.Compute/virtualMachines",
            [...]
            "properties": {
                [...]
                "storageProfile": {
                    [...]
                    "dataDisks": "[if(equals(length(parameters('dataDiskArray')),0),json('null'),variables('dataDisks'))]"
                },
                [...]
                }
            }
    ],
    "outputs": {
    }
}