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Resource iteration in ARM templates

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This article shows you how to create more than one instance of a resource in your Azure Resource Manager template (ARM template). By adding copy loop to the resources section of your template, you can dynamically set the number of resources to deploy. You also avoid having to repeat template syntax.

You can also use copy loop with properties, variables, and outputs.

If you need to specify whether a resource is deployed at all, see condition element.

Tip

We recommend Bicep because it offers the same capabilities as ARM templates and the syntax is easier to use. To learn more, see loops.

Syntax

Add the copy element to the resources section of your template to deploy multiple instances of the resource. The copy element has the following general format:

"copy": {
  "name": "<name-of-loop>",
  "count": <number-of-iterations>,
  "mode": "serial" <or> "parallel",
  "batchSize": <number-to-deploy-serially>
}

The name property is any value that identifies the loop. The count property specifies the number of iterations you want for the resource type.

Use the mode and batchSize properties to specify if the resources are deployed in parallel or in sequence. These properties are described in Serial or Parallel.

Copy limits

The count can't exceed 800.

The count can't be a negative number. It can be zero if you deploy the template with a recent version of Azure CLI, PowerShell, or REST API. Specifically, you must use:

  • Azure PowerShell 2.6 or later
  • Azure CLI 2.0.74 or later
  • REST API version 2019-05-10 or later
  • Linked deployments must use API version 2019-05-10 or later for the deployment resource type

Earlier versions of PowerShell, CLI, and the REST API don't support zero for count.

Be careful using complete mode deployment with copy loop. If you redeploy with complete mode to a resource group, any resources that aren't specified in the template after resolving the copy loop are deleted.

Resource iteration

The following example creates the number of storage accounts specified in the storageCount parameter.

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "location": {
      "type": "string",
      "defaultValue": "[resourceGroup().location]"
    },
    "storageCount": {
      "type": "int",
      "defaultValue": 3
    }
  },
  "resources": [
    {
      "copy": {
        "name": "storagecopy",
        "count": "[length(range(0, parameters('storageCount')))]"
      },
      "type": "Microsoft.Storage/storageAccounts",
      "apiVersion": "2022-09-01",
      "name": "[format('{0}storage{1}', range(0, parameters('storageCount'))[copyIndex()], uniqueString(resourceGroup().id))]",
      "location": "[parameters('location')]",
      "sku": {
        "name": "Standard_LRS"
      },
      "kind": "Storage",
      "properties": {}
    }
  ]
}

Notice that the name of each resource includes the copyIndex() function, which returns the current iteration in the loop. copyIndex() is zero-based. So, the following example:

"name": "[format('storage{0}', copyIndex())]",

Creates these names:

  • storage0
  • storage1
  • storage2

To offset the index value, you can pass a value in the copyIndex() function. The number of iterations is still specified in the copy element, but the value of copyIndex is offset by the specified value. So, the following example:

"name": "[format('storage{0}', copyIndex(1))]",

Creates these names:

  • storage1
  • storage2
  • storage3

The copy operation is helpful when working with arrays because you can iterate through each element in the array. Use the length function on the array to specify the count for iterations, and copyIndex to retrieve the current index in the array.

The following example creates one storage account for each name provided in the parameter.

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "storageNames": {
      "type": "array",
      "defaultValue": [
        "contoso",
        "fabrikam",
        "coho"
      ]
    },
    "location": {
      "type": "string",
      "defaultValue": "[resourceGroup().location]"
    }
  },
  "resources": [
    {
      "copy": {
        "name": "storagecopy",
        "count": "[length(parameters('storageNames'))]"
      },
      "type": "Microsoft.Storage/storageAccounts",
      "apiVersion": "2022-09-01",
      "name": "[format('{0}{1}', parameters('storageNames')[copyIndex()], uniqueString(resourceGroup().id))]",
      "location": "[parameters('location')]",
      "sku": {
        "name": "Standard_LRS"
      },
      "kind": "Storage",
      "properties": {}
    }
  ]
}

If you want to return values from the deployed resources, you can use copy in the outputs section.

Use symbolic name

Symbolic name will be assigned to resource copy loops. The loop index is zero-based. In the following example, myStorages[1] references the second resource in the resource loop.

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "languageVersion": "2.0",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "location": {
      "type": "string",
      "defaultValue": "[resourceGroup().location]"
    },
    "storageCount": {
      "type": "int",
      "defaultValue": 2
    }
  },
  "resources": {
    "myStorages": {
      "type": "Microsoft.Storage/storageAccounts",
      "apiVersion": "2022-09-01",
      "name": "[format('{0}storage{1}', copyIndex(), uniqueString(resourceGroup().id))]",
      "location": "[parameters('location')]",
      "sku": {
        "name": "Standard_LRS"
      },
      "kind": "Storage",
      "properties": {},
      "copy": {
        "name": "storagecopy",
        "count": "[parameters('storageCount')]"
      }
    }
  },
  "outputs": {
    "storageEndpoint":{
      "type": "object",
      "value": "[reference('myStorages[1]').primaryEndpoints]"
    }
  }
}

If the index is a runtime value, format the reference yourself. For example

"outputs": {
  "storageEndpoint":{
    "type": "object",
    "value": "[reference(format('myStorages[{0}]', variables('runtimeIndex'))).primaryEndpoints]"
  }
}

Symbolic names can be used in dependsOn arrays. If a symbolic name is for a copy loop, all resources in the loop are added as dependencies. For more information, see Depends on resources in a loop.

Serial or Parallel

By default, Resource Manager creates the resources in parallel. It applies no limit to the number of resources deployed in parallel, other than the total limit of 800 resources in the template. The order in which they're created isn't guaranteed.

However, you may want to specify that the resources are deployed in sequence. For example, when updating a production environment, you may want to stagger the updates so only a certain number are updated at any one time.

To serially deploy more than one instance of a resource, set mode to serial and batchSize to the number of instances to deploy at a time. With serial mode, Resource Manager creates a dependency on earlier instances in the loop, so it doesn't start one batch until the previous batch completes.

The value for batchSize can't exceed the value for count in the copy element.

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "location": {
      "type": "string",
      "defaultValue": "[resourceGroup().location]"
    }
  },
  "resources": [
    {
      "copy": {
        "name": "storagecopy",
        "count": 4,
        "mode": "serial",
        "batchSize": 2
      },
      "type": "Microsoft.Storage/storageAccounts",
      "apiVersion": "2022-09-01",
      "name": "[format('{0}storage{1}', range(0, 4)[copyIndex()], uniqueString(resourceGroup().id))]",
      "location": "[parameters('location')]",
      "sku": {
        "name": "Standard_LRS"
      },
      "kind": "Storage",
      "properties": {}
    }
  ]
}

The mode property also accepts parallel, which is the default value.

Iteration for a child resource

You can't use a copy loop for a child resource. To create more than one instance of a resource that you typically define as nested within another resource, you must instead create that resource as a top-level resource. You define the relationship with the parent resource through the type and name properties.

For example, suppose you typically define a dataset as a child resource within a data factory.

{
  "resources": [
    {
      "type": "Microsoft.DataFactory/factories",
      "name": "exampleDataFactory",
      ...
      "resources": [
        {
          "type": "datasets",
          "name": "exampleDataSet",
          "dependsOn": [
            "exampleDataFactory"
          ],
          ...
        }
      ]
      ...
    }
  ]
}

To create more than one data set, move it outside of the data factory. The dataset must be at the same level as the data factory, but it's still a child resource of the data factory. You preserve the relationship between data set and data factory through the type and name properties. Since type can no longer be inferred from its position in the template, you must provide the fully qualified type in the format: {resource-provider-namespace}/{parent-resource-type}/{child-resource-type}.

To establish a parent/child relationship with an instance of the data factory, provide a name for the data set that includes the parent resource name. Use the format: {parent-resource-name}/{child-resource-name}.

The following example shows the implementation.

"resources": [
{
  "type": "Microsoft.DataFactory/factories",
  "name": "exampleDataFactory",
  ...
},
{
  "type": "Microsoft.DataFactory/factories/datasets",
  "name": "[format('exampleDataFactory/exampleDataSet{0}', copyIndex())]",
  "dependsOn": [
    "exampleDataFactory"
  ],
  "copy": {
    "name": "datasetcopy",
    "count": "3"
  },
  ...
}]

Example templates

The following examples show common scenarios for creating more than one instance of a resource or property.

Template Description
Copy storage Deploys more than one storage account with an index number in the name.
Serial copy storage Deploys several storage accounts one at time. The name includes the index number.
Copy storage with array Deploys several storage accounts. The name includes a value from an array.
Copy resource group Deploys multiple resource groups.

Next steps