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ARM template parameters and variables in Azure - Commands & Configuration

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Introduction
When creating resources in Azure, you often need to customize settings without changing the whole template. Parameters and variables help you reuse templates by allowing input values and storing reusable data inside the template.
When you want to deploy the same infrastructure with different names or sizes without editing the template each time
When you need to keep some values fixed inside the template for reuse, like location or tags
When you want to make your template easier to read and maintain by separating input values from fixed values
When you want to share a template with others and let them provide their own settings
When you want to avoid repeating the same value multiple times inside the template
Config File - azuredeploy.json
azuredeploy.json
{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "parameters": {
    "storageAccountName": {
      "type": "string",
      "metadata": {
        "description": "Name of the storage account"
      }
    },
    "location": {
      "type": "string",
      "defaultValue": "eastus",
      "metadata": {
        "description": "Location for all resources"
      }
    }
  },
  "variables": {
    "storageAccountType": "Standard_LRS",
    "storageAccountId": "[resourceId('Microsoft.Storage/storageAccounts', parameters('storageAccountName'))]"
  },
  "resources": [
    {
      "type": "Microsoft.Storage/storageAccounts",
      "apiVersion": "2022-09-01",
      "name": "[parameters('storageAccountName')]",
      "location": "[parameters('location')]",
      "sku": {
        "name": "[variables('storageAccountType')]"
      },
      "kind": "StorageV2",
      "properties": {}
    }
  ],
  "outputs": {
    "storageAccountResourceId": {
      "type": "string",
      "value": "[variables('storageAccountId')]"
    }
  }
}

parameters: Define inputs you provide when deploying, like storage account name and location.

variables: Store fixed or computed values used inside the template, like the storage account type and resource ID.

resources: Define the Azure resources to create, using parameters and variables for configuration.

outputs: Return useful information after deployment, here the resource ID of the storage account.

Commands
This command deploys the ARM template to the resource group 'example-rg' using the template file. It sets the storage account name parameter to 'examplestorage123'.
Terminal
az deployment group create --resource-group example-rg --template-file azuredeploy.json --parameters storageAccountName=examplestorage123
Expected OutputExpected
{ "id": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/example-rg/providers/Microsoft.Resources/deployments/deployment1", "name": "deployment1", "properties": { "provisioningState": "Succeeded", "outputs": { "storageAccountResourceId": { "type": "String", "value": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/example-rg/providers/Microsoft.Storage/storageAccounts/examplestorage123" } } }, "type": "Microsoft.Resources/deployments" }
→
--resource-group - Specifies the Azure resource group to deploy to
→
--template-file - Specifies the ARM template file to use
→
--parameters - Sets the input parameters for the template
This command shows details about the deployment named 'deployment1' in the resource group 'example-rg' to verify the deployment status and outputs.
Terminal
az deployment group show --resource-group example-rg --name deployment1
Expected OutputExpected
{ "name": "deployment1", "properties": { "provisioningState": "Succeeded", "outputs": { "storageAccountResourceId": { "type": "String", "value": "/subscriptions/00000000-0000-0000-0000-000000000000/resourceGroups/example-rg/providers/Microsoft.Storage/storageAccounts/examplestorage123" } } } }
→
--resource-group - Specifies the resource group of the deployment
→
--name - Specifies the deployment name to query
Key Concept

If you remember nothing else from this pattern, remember: parameters let you customize your template inputs, and variables let you reuse fixed or computed values inside the template.

Common Mistakes
Not providing required parameters when deploying the template
The deployment fails because the template expects input values that are missing
Always provide values for all required parameters either via command line or a parameters file
Trying to use variables as parameters or vice versa
Parameters are inputs from outside, variables are internal; mixing them causes errors or unexpected behavior
Use parameters for inputs you want to change at deployment time, variables for fixed or computed values inside the template
Summary
Define parameters in the ARM template to accept input values at deployment time.
Use variables to store fixed or computed values for reuse inside the template.
Deploy the template with parameters using the Azure CLI and verify the deployment outputs.

Practice

(1/5)
1.

What is the main purpose of parameters in an ARM template?

easy
A. To define the resources to deploy
B. To allow input values when deploying the template
C. To store fixed values inside the template
D. To specify deployment location only

Solution

  1. Step 1: Understand parameters role

    Parameters let users provide input values at deployment time, making templates flexible.

  2. Step 2: Differentiate from variables

    Variables store fixed or computed values inside the template, not input values.

  3. Final Answer:

    To allow input values when deploying the template -> Option B

  4. Quick Check:

    Parameters = input values [OK]
Hint: Parameters accept inputs during deployment, variables do not [OK]
Common Mistakes:
  • Confusing parameters with variables
  • Thinking parameters define resources
  • Assuming parameters are fixed values
2.

Which of the following is the correct syntax to declare a variable named storageAccountName in an ARM template?

{
  "variables": {
    "storageAccountName": "myStorage"
  }
}
easy
A. "resources": { "storageAccountName": "myStorage" }
B. "parameters": { "storageAccountName": "myStorage" }
C. "variables": { "storageAccountName": "myStorage" }
D. "outputs": { "storageAccountName": "myStorage" }

Solution

  1. Step 1: Identify variable declaration section

    Variables are declared inside the "variables" section as key-value pairs.

  2. Step 2: Match syntax with example

    The example shows "variables": { "storageAccountName": "myStorage" }, which matches "variables": { "storageAccountName": "myStorage" }.

  3. Final Answer:

    "variables": { "storageAccountName": "myStorage" } -> Option C

  4. Quick Check:

    Variables declared under "variables" [OK]
Hint: Variables go inside "variables" block, not parameters or resources [OK]
Common Mistakes:
  • Putting variables inside parameters
  • Confusing variables with outputs
  • Using wrong JSON section names
3.

Given this ARM template snippet, what will be the value of variables('fullName')?

{
  "parameters": {
    "firstName": { "type": "string", "defaultValue": "John" },
    "lastName": { "type": "string", "defaultValue": "Doe" }
  },
  "variables": {
    "fullName": "[concat(parameters('firstName'), ' ', parameters('lastName'))]"
  }
}
medium
A. parameters('firstName') parameters('lastName')
B. JohnDoe
C. [concat(parameters('firstName'), ' ', parameters('lastName'))]
D. John Doe

Solution

  1. Step 1: Understand concat function in variables

    The variable "fullName" uses concat to join firstName, a space, and lastName.

  2. Step 2: Substitute default parameter values

    firstName = "John", lastName = "Doe", so concat("John", " ", "Doe") = "John Doe".

  3. Final Answer:

    John Doe -> Option D

  4. Quick Check:

    concat with space joins names [OK]
Hint: concat joins strings; default parameters fill in values [OK]
Common Mistakes:
  • Taking concat as literal string
  • Ignoring space between names
  • Confusing parameters with variables
4.

Identify the error in this ARM template snippet:

{
  "parameters": {
    "location": { "type": "string" }
  },
  "variables": {
    "region": "parameters('location')"
  }
}
medium
A. Missing square brackets around the parameter reference in variable
B. Variable names cannot be 'region'
C. Parameter type must be 'securestring' to use in variables
D. Variables cannot reference parameters

Solution

  1. Step 1: Check variable referencing syntax

    Variables referencing parameters must use expression syntax with square brackets: "[parameters('location')]".

  2. Step 2: Identify missing brackets

    The variable "region" is assigned "parameters('location')" as a string, not an expression.

  3. Final Answer:

    Missing square brackets around the parameter reference in variable -> Option A

  4. Quick Check:

    Parameter references need [ ] in variables [OK]
Hint: Use [parameters('name')] inside variables, not plain strings [OK]
Common Mistakes:
  • Omitting square brackets for expressions
  • Thinking variables can't use parameters
  • Wrong parameter types for variables
5.

You want to create an ARM template that deploys a storage account with a name based on a parameter prefix and a variable uniqueString. Which is the best way to combine them in the template?

{
  "parameters": {
    "prefix": { "type": "string" }
  },
  "variables": {
    "uniqueString": "[uniqueString(resourceGroup().id)]"
  },
  "resources": [
    {
      "type": "Microsoft.Storage/storageAccounts",
      "name": "???",
      "apiVersion": "2022-09-01",
      "location": "[resourceGroup().location]"
    }
  ]
}

Choose the correct expression to use for the storage account name property.

hard
A. "[concat(parameters('prefix'), variables('uniqueString'))]"
B. "parameters('prefix') + variables('uniqueString')"
C. "[parameters('prefix') variables('uniqueString')]"
D. "concat(parameters.prefix, variables.uniqueString)"

Solution

  1. Step 1: Understand ARM template expression syntax

    Expressions must be inside square brackets and use functions like concat() to join strings.

  2. Step 2: Check correct usage of parameters and variables

    Use parameters('name') and variables('name') inside concat() within brackets.

  3. Step 3: Evaluate options

    "[concat(parameters('prefix'), variables('uniqueString'))]" uses correct syntax: "[concat(parameters('prefix'), variables('uniqueString'))]".

  4. Final Answer:

    "[concat(parameters('prefix'), variables('uniqueString'))]" -> Option A

  5. Quick Check:

    Use [concat(parameters('x'), variables('y'))] for combined names [OK]
Hint: Use [concat(parameters('x'), variables('y'))] for combined strings [OK]
Common Mistakes:
  • Using + instead of concat inside brackets
  • Omitting square brackets for expressions
  • Wrong syntax for parameters or variables
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