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Use objects as parameters in a copy loop in an Azure Resource Manager template

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When you use objects as parameters in Azure Resource Manager templates (ARM templates), you can include them in a copy loop. This technique is very useful when it's combined with a serial copy loop, especially for deploying child resources.

To demonstrate this approach, let's look at a template that deploys a network security group (NSG) with two security rules.

First, let's look at our parameters. When we look at our template we see that we defined one parameter named networkSecurityGroupsSettings that includes an array named securityRules. This array contains two JSON objects, each of which specifies settings that define a security rule.

{
    "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentParameters.json#",
    "contentVersion": "1.0.0.0",
    "parameters":{
        "networkSecurityGroupsSettings": {
            "value": {
                "securityRules": [
                    {
                        "name": "RDPAllow",
                        "description": "allow RDP connections",
                        "direction": "Inbound",
                        "priority": 100,
                        "sourceAddressPrefix": "*",
                        "destinationAddressPrefix": "10.0.0.0/24",
                        "sourcePortRange": "*",
                        "destinationPortRange": "3389",
                        "access": "Allow",
                        "protocol": "Tcp"
                    },
                    {
                        "name": "HTTPAllow",
                        "description": "allow HTTP connections",
                        "direction": "Inbound",
                        "priority": 200,
                        "sourceAddressPrefix": "*",
                        "destinationAddressPrefix": "10.0.1.0/24",
                        "sourcePortRange": "*",
                        "destinationPortRange": "80",
                        "access": "Allow",
                        "protocol": "Tcp"
                    }
                ]
            }
        }
    }
}

Now, let's look at our template. We have a resource named NSG1 that deploys the NSG. It also uses ARM's built-in property iteration feature. By adding copy loop to the properties section of a resource in your template, you can dynamically set the number of items for a property during deployment. You also avoid having to repeat template syntax.

{
    "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
    "contentVersion": "1.0.0.0",
    "parameters": {
        "VNetSettings": {
            "type": "object"
        },
        "networkSecurityGroupsSettings": {
            "type": "object"
        }
    },
    "resources": [
        {
            "apiVersion": "2020-05-01",
            "type": "Microsoft.Network/virtualNetworks",
            "name": "[parameters('VNetSettings').name]",
            "location": "[resourceGroup().location]",
            "properties": {
                "addressSpace": {
                    "addressPrefixes": [
                        "[parameters('VNetSettings').addressPrefixes[0].addressPrefix]"
                    ]
                },
                "subnets": [
                    {
                        "name": "[parameters('VNetSettings').subnets[0].name]",
                        "properties": {
                            "addressPrefix": "[parameters('VNetSettings').subnets[0].addressPrefix]"
                        }
                    },
                    {
                        "name": "[parameters('VNetSettings').subnets[1].name]",
                        "properties": {
                            "addressPrefix": "[parameters('VNetSettings').subnets[1].addressPrefix]"
                        }
                    }
                ]
            }
        },
        {
            "apiVersion": "2020-05-01",
            "type": "Microsoft.Network/networkSecurityGroups",
            "name": "NSG1",
            "location": "[resourceGroup().location]",
            "properties": {
                "copy": [
                    {
                        "name": "securityRules",
                        "count": "[length(parameters('networkSecurityGroupsSettings').securityRules)]",
                        "input": {
                            "name": "[parameters('networkSecurityGroupsSettings').securityRules[copyIndex('securityRules')].name]",
                            "properties": {

                                "description": "[parameters('networkSecurityGroupsSettings').securityRules[copyIndex('securityRules')].description]",
                                "priority": "[parameters('networkSecurityGroupsSettings').securityRules[copyIndex('securityRules')].priority]",
                                "protocol": "[parameters('networkSecurityGroupsSettings').securityRules[copyIndex('securityRules')].protocol]",
                                "sourcePortRange": "[parameters('networkSecurityGroupsSettings').securityRules[copyIndex('securityRules')].sourcePortRange]",
                                "destinationPortRange": "[parameters('networkSecurityGroupsSettings').securityRules[copyIndex('securityRules')].destinationPortRange]",
                                "sourceAddressPrefix": "[parameters('networkSecurityGroupsSettings').securityRules[copyIndex('securityRules')].sourceAddressPrefix]",
                                "destinationAddressPrefix": "[parameters('networkSecurityGroupsSettings').securityRules[copyIndex('securityRules')].destinationAddressPrefix]",
                                "access": "[parameters('networkSecurityGroupsSettings').securityRules[copyIndex('securityRules')].access]",
                                "direction": "[parameters('networkSecurityGroupsSettings').securityRules[copyIndex('securityRules')].direction]"
                            }
                        }
                    }
                ]
            }
        }
    ]
}

Let's take a closer look at how we specify our property values in the securityRules child resource. All of our properties are referenced by using the parameters() function. Then we use the dot operator to reference our securityRules array, and index it by the current value of the iteration. Finally, we use another dot operator to reference the name of the object.

Try the template

An example template is available on GitHub. To deploy the template, clone the repo and run the following Azure CLI commands:

git clone https://github.com/mspnp/template-examples.git
cd template-examples/example3-object-param
az group create --location <location> --name <resource-group-name>
az deployment group create -g <resource-group-name> \
    --template-uri https://raw.githubusercontent.com/mspnp/template-examples/master/example3-object-param/deploy.json \
    --parameters deploy.parameters.json

Next steps