Using Functions and Expressions in ARM Templates | Azure ARM Tutorial

Welcome to the tutorial on using functions and expressions in ARM templates for Azure Resource Manager. ARM templates provide a powerful way to define and deploy infrastructure and applications in Azure. Functions and expressions allow you to perform complex operations and transformations within your templates, making them more dynamic and adaptable.

1. Using Functions

Functions in ARM templates enable you to perform various operations and calculations. They can be used to generate unique names, concatenate strings, retrieve property values, and more. Functions are invoked using the functionName() syntax.


"resources": [
  {
    "type": "Microsoft.Storage/storageAccounts",
    "name": "[concat('mystorageaccount', uniqueString(resourceGroup().id))]",
    "apiVersion": "2021-04-01",
    ...
  }
]

2. Using Expressions

Expressions in ARM templates allow you to evaluate and manipulate values based on the context of the deployment. They can be used to reference variables, parameters, resource properties, and functions. Expressions are enclosed within square brackets.


"resources": [
  {
    "type": "Microsoft.Network/networkInterfaces",
    "name": "[concat(parameters('nicNamePrefix'), copyIndex())]",
    "apiVersion": "2021-02-01",
    ...
  }
]

3. Steps to Use Functions and Expressions

Follow these steps to utilize functions and expressions in your ARM templates:

Step 1: Understand Available Functions

Review the list of available functions in the Azure documentation to determine which functions are relevant to your scenario. Functions cover various areas such as string manipulation, mathematical calculations, resource management, and more.

Step 2: Invoke Functions

Invoke functions within your ARM template using the functionName() syntax. Pass any required parameters within the parentheses.


"resources": [
  {
    "type": "Microsoft.Compute/virtualMachines",
    "name": "[concat('myVM', uniqueString(subscription().id, resourceGroup().id))]",
    "apiVersion": "2021-03-01",
    ...
  }
]

Step 3: Use Expressions

Enclose expressions within square brackets [] to dynamically evaluate and manipulate values. Expressions can reference functions, variables, parameters, and resource properties.


"resources": [
  {
    "type": "Microsoft.Storage/storageAccounts",
    "name": "[concat('mystorageaccount-', uniqueString(resourceGroup().id))]",
    "apiVersion": "2021-04-01",
    ...
  }
]

Mistakes to Avoid

Using incorrect syntax for invoking functions or enclosing expressions.
Forgetting to pass required parameters to functions.
Not checking the available functions and using custom functions that are not supported in ARM templates.

Frequently Asked Questions (FAQs)

Q: Can I create custom functions in ARM templates?
A: No, ARM templates do not support the creation of custom functions. You can only use the predefined functions provided by Azure.
Q: Can I nest functions within expressions?
A: Yes, you can nest functions within expressions to perform complex operations. Ensure that you follow the correct syntax and order of function invocations.
Q: Can I use functions to retrieve resource properties?
A: Yes, functions like reference() can be used to retrieve properties of existing resources within your ARM template.
Q: Can I use expressions to conditionally deploy resources?
A: Yes, expressions can be used to define conditions for resource deployment. By using functions like if() or equals(), you can control the creation of resources based on specific criteria.
Q: Are there any limitations on using functions and expressions in ARM templates?
A: Yes, there are certain limitations on the usage of functions and expressions in ARM templates. It's recommended to refer to the official Azure documentation for detailed information on the limitations and available functions.

Summary

In this tutorial, you learned how to use functions and expressions in ARM templates for Azure Resource Manager. Functions enable you to perform various operations, while expressions allow you to dynamically evaluate and manipulate values within your templates. By leveraging functions and expressions effectively, you can create more flexible and dynamic ARM templates for your Azure deployments.