Tutorial: Add variables to your ARM template

Article
07/28/2023

In this tutorial, you learn how to add a variable to your Azure Resource Manager template (ARM template). Variables simplify your templates. They let you write an expression once and reuse it throughout the template. This tutorial takes 7 minutes to complete.

Prerequisites

We recommend that you complete the tutorial about functions, but it's not required.

You need to have Visual Studio Code installed and working with the Azure Resource Manager Tools extension, and either Azure PowerShell or Azure CLI. For more information, see template tools.

Review template

At the end of the previous tutorial, your template had the following JSON file:

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "storageName": {
      "type": "string",
      "minLength": 3,
      "maxLength": 24
    },
    "storageSKU": {
      "type": "string",
      "defaultValue": "Standard_LRS",
      "allowedValues": [
        "Standard_LRS",
        "Standard_GRS",
        "Standard_RAGRS",
        "Standard_ZRS",
        "Premium_LRS",
        "Premium_ZRS",
        "Standard_GZRS",
        "Standard_RAGZRS"
      ]
    },
    "location": {
      "type": "string",
      "defaultValue": "[resourceGroup().location]"
    }
  },
  "resources": [
    {
      "type": "Microsoft.Storage/storageAccounts",
      "apiVersion": "2021-09-01",
      "name": "[parameters('storageName')]",
      "location": "[parameters('location')]",
      "sku": {
        "name": "[parameters('storageSKU')]"
      },
      "kind": "StorageV2",
      "properties": {
        "supportsHttpsTrafficOnly": true
      }
    }
  ]
}

Your Azure storage account name needs to be unique to easily continue to build your ARM template. If you've completed the earlier tutorials in this series, you're tired of coming up with a unique name. You solve this problem by adding a variable that creates a unique name for your storage account.

Use variable

The following example highlights the changes to add a variable to your template that creates a unique storage account name. Copy the whole file and replace your template with its contents.

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "storagePrefix": {
      "type": "string",
      "minLength": 3,
      "maxLength": 11
    },
    "storageSKU": {
      "type": "string",
      "defaultValue": "Standard_LRS",
      "allowedValues": [
        "Standard_LRS",
        "Standard_GRS",
        "Standard_RAGRS",
        "Standard_ZRS",
        "Premium_LRS",
        "Premium_ZRS",
        "Standard_GZRS",
        "Standard_RAGZRS"
      ]
    },
    "location": {
      "type": "string",
      "defaultValue": "[resourceGroup().location]"
    }
  },
  "variables": {
    "uniqueStorageName": "[concat(parameters('storagePrefix'), uniqueString(resourceGroup().id))]"
  },
  "resources": [
    {
      "type": "Microsoft.Storage/storageAccounts",
      "apiVersion": "2021-09-01",
      "name": "[variables('uniqueStorageName')]",
      "location": "[parameters('location')]",
      "sku": {
        "name": "[parameters('storageSKU')]"
      },
      "kind": "StorageV2",
      "properties": {
        "supportsHttpsTrafficOnly": true
      }
    }
  ]
}

Notice that it includes a variable named uniqueStorageName. This variable uses four functions to create a string value.

You're already familiar with the parameters function, so we won't examine it.

You're also familiar with the resourceGroup function. In this case, you get the id property instead of the location property, as shown in the previous tutorial. The id property returns the full identifier of the resource group, including the subscription ID and the resource group name.

The uniqueString function creates a 13-character hash value. The parameters you pass determine the returned value. For this tutorial, you use the resource group ID as the input for the hash value. That means you could deploy this template to different resource groups and get a different unique string value. You get the same value, however, if you deploy to the same resource group.

The concat function takes values and combines them. For this variable, it takes the string from the parameter and the string from the uniqueString function and combines them into one string.

The storagePrefix parameter lets you pass in a prefix that helps you identify storage accounts. You can create your own naming convention that makes it easier to identify storage accounts after deployment from an extensive list of resources.

Finally, notice that the storage account name is now set to the variable instead of a parameter.

Deploy template

Let's deploy the template. Deploying this template is easier than the previous templates because you provide just the prefix for the storage account name.

If you haven't created the resource group, see Create resource group. The example assumes you've set the templateFile variable to the path to the template file, as shown in the first tutorial.

PowerShell
Azure CLI

New-AzResourceGroupDeployment `
  -Name addnamevariable `
  -ResourceGroupName myResourceGroup `
  -TemplateFile $templateFile `
  -storagePrefix "store" `
  -storageSKU Standard_LRS

To run this deployment command, you need to have the latest version of Azure CLI.

az deployment group create \
  --name addnamevariable \
  --resource-group myResourceGroup \
  --template-file $templateFile \
  --parameters '{"storagePrefix": {"value":"store"}}' '{"storageSKU": {"value":"Standard_LRS"}}'

Note

If the deployment fails, use the verbose switch to get information about the resources being created. Use the debug switch to get more information for debugging.

Verify deployment

You can verify the deployment by exploring the resource group from the Azure portal.

Sign in to the Azure portal.
From the left menu, select Resource groups.
Select your resource group.
Notice your deployed storage account name is store, plus a string of random characters.

Clean up resources

If you're moving on to the next tutorial, you don't need to delete the resource group.

If you're stopping now, you might want to delete the resource group.

From the Azure portal, select Resource groups from the left menu.
Type the resource group name in the Filter for any field... text field.
Check the box next to myResourceGroup and select myResourceGroup or your resource group name.
Select Delete resource group from the top menu.

Next steps

In this tutorial, you add a variable that creates a unique storage account name. In the next tutorial, you return a value from the deployed storage account.

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