ARM template outputs in Azure - Mini Project: Build & Apply

ARM Template Outputs

📖 Scenario: You are deploying a simple Azure storage account using an ARM template. You want to see the storage account's name and primary endpoint as outputs after deployment.

🎯 Goal: Create an ARM template that defines a storage account resource and includes outputs for the storage account name and its primary blob endpoint.

📋 What You'll Learn

Define a storage account resource with a fixed name

Add outputs for the storage account name and primary blob endpoint

Use correct ARM template syntax for outputs

💡 Why This Matters

🌍 Real World

ARM templates are used to automate Azure resource deployments consistently and repeatedly.

💼 Career

Knowing how to write ARM templates with outputs is essential for Azure cloud engineers and DevOps professionals to manage infrastructure as code.

1

Create the ARM template skeleton

Create a JSON ARM template with schema set to "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#" and an empty resources array.

Azure

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": []
  // Your code here
}

Hint

Start with the basic ARM template structure including $schema, contentVersion, and an empty resources array.

2

Add a storage account resource

Add a resource of type Microsoft.Storage/storageAccounts with name examplestorageacct, location eastus, and sku name Standard_LRS. Use kind as StorageV2 and set apiVersion to 2021-04-01.

Azure

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [
    {
      // Your code here
    }
  ]
}

Hint

Define the storage account resource with the required properties inside the resources array.

3

Add outputs for storage account name and primary blob endpoint

Add an outputs section with two outputs: storageAccountName that returns the storage account name using reference, and primaryBlobEndpoint that returns the primary blob endpoint from the storage account's primaryEndpoints.blob property.

Azure

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [
    {
      "type": "Microsoft.Storage/storageAccounts",
      "apiVersion": "2021-04-01",
      "name": "examplestorageacct",
      "location": "eastus",
      "sku": {
        "name": "Standard_LRS"
      },
      "kind": "StorageV2",
      "properties": {}
    }
  ],
  "outputs": {
    // Your code here
  }
}

Hint

Use the outputs section to expose values after deployment. Use reference() to get resource properties.

4

Complete the ARM template with correct JSON structure

Ensure the ARM template JSON is valid and includes $schema, contentVersion, resources with the storage account, and outputs with the storage account name and primary blob endpoint.

Azure

{
  "$schema": "https://schema.management.azure.com/schemas/2019-04-01/deploymentTemplate.json#",
  "contentVersion": "1.0.0.0",
  "resources": [
    {
      "type": "Microsoft.Storage/storageAccounts",
      "apiVersion": "2021-04-01",
      "name": "examplestorageacct",
      "location": "eastus",
      "sku": {
        "name": "Standard_LRS"
      },
      "kind": "StorageV2",
      "properties": {}
    }
  ],
  "outputs": {
    "storageAccountName": {
      "type": "string",
      "value": "[reference('examplestorageacct').name]"
    },
    "primaryBlobEndpoint": {
      "type": "string",
      "value": "[reference('examplestorageacct').primaryEndpoints.blob]"
    }
  }
  // Your code here
}

Hint

Check that the JSON is complete and valid with all required sections.

Practice

1. What is the main purpose of outputs in an ARM template?

easy

A. To display important information after deployment

B. To define the resources to deploy

C. To specify deployment parameters

D. To set access permissions for resources

Solution

1. Step 1: Understand the role of outputs in ARM templates

   Outputs are used to show key information after the deployment finishes, such as resource IDs or connection strings.

2. Step 2: Differentiate outputs from other template sections

   Resources define what to deploy, parameters set inputs, and outputs show results after deployment.

3. Final Answer:

   To display important information after deployment -> Option A

4. Quick Check:

   Outputs = show info after deployment [OK]

Hint: Outputs always show info after deployment [OK]

Common Mistakes:

• Confusing outputs with parameters
• Thinking outputs define resources
• Assuming outputs set permissions

2. Which of the following is the correct syntax to define an output named storageAccountName of type string in an ARM template?

easy

A. "outputs": { "storageAccountName": { "type": "string", "val": "[variables('storageName')]" } }

B. "outputs": { "storageAccountName": { "type": "string", "value": "[variables('storageName')]" } }

C. "outputs": { "storageAccountName": { "datatype": "string", "value": "[variables('storageName')]" } }

D. "outputs": { "storageAccountName": { "type": "string", "value": "variables('storageName')" } }

Solution

1. Step 1: Check the required keys for output

   An output must have a "type" key specifying the data type and a "value" key with an expression or value.

2. Step 2: Validate the syntax for referencing variables

   The value must be an expression in square brackets, e.g., "[variables('storageName')]".

3. Final Answer:

   "outputs": { "storageAccountName": { "type": "string", "value": "[variables('storageName')]" } } -> Option B

4. Quick Check:

   Output syntax = type + value with [expression] [OK]

Hint: Outputs need "type" and "value" keys with expressions in brackets [OK]

Common Mistakes:

• Using 'datatype' instead of 'type'
• Using 'val' instead of 'value'
• Missing brackets around expressions

3. Given this output snippet in an ARM template:

"outputs": { "appEndpoint": { "type": "string", "value": "[concat('https://', reference(resourceId('Microsoft.Web/sites', variables('appName'))).defaultHostName)]" }}

What will appEndpoint output after deployment?

medium

A. The app name only

B. The resource ID of the web app

C. The full URL of the deployed web app

D. An error because of wrong syntax

Solution

1. Step 1: Understand the expression used in the output value

   The expression uses concat to build a URL string starting with 'https://' and appends the defaultHostName property of the web app resource.

2. Step 2: Determine what reference() returns

   reference() fetches runtime properties of the deployed resource, here the web app's hostname.

3. Final Answer:

   The full URL of the deployed web app -> Option C

4. Quick Check:

   Output builds URL using reference() = full URL [OK]

Hint: reference() gets deployed resource info, concat builds URL [OK]

Common Mistakes:

• Thinking output returns resource ID instead of hostname
• Confusing variable name with output value
• Assuming syntax error due to complex expression

4. You have this output defined:

"outputs": { "storageKey": { "type": "string", "value": "listKeys(resourceId('Microsoft.Storage/storageAccounts', variables('storageName')), '2021-04-01').keys[0].value" }}

After deployment, you get an error. What is the likely cause?

medium

A. Missing square brackets around the expression value

B. Incorrect API version in listKeys function

C. Output type should be 'securestring' instead of 'string'

D. Variables section missing the storageName variable

Solution

1. Step 1: Check the syntax for output value expressions

   Output values must be enclosed in square brackets to indicate an expression, e.g., "[expression]".

2. Step 2: Identify the missing brackets in the given output

   The value is missing the surrounding brackets, so ARM treats it as a literal string causing an error.

3. Final Answer:

   Missing square brackets around the expression value -> Option A

4. Quick Check:

   Output expressions need [ ] brackets [OK]

Hint: Always wrap output expressions in [ ] brackets [OK]

Common Mistakes:

• Forgetting brackets around expressions
• Assuming API version is wrong without checking
• Confusing output type with expression syntax

5. You want to output a list of VM names created by a loop in your ARM template. Which output definition correctly returns an array of VM names?

hard

A. "outputs": { "vmNames": { "type": "array", "value": "[array(variables('vmNames'))]" } }

B. "outputs": { "vmNames": { "type": "object", "value": "variables('vmNames')" } }

C. "outputs": { "vmNames": { "type": "string", "value": "[variables('vmNames')]" } }

D. "outputs": { "vmNames": { "type": "array", "value": "[variables('vmNames')]" } }

Solution

1. Step 1: Identify the correct output type for a list of names

   A list of VM names is an array, so the output type should be "array".

2. Step 2: Check the syntax for output value expressions

   The value must be an expression enclosed in brackets, e.g., "[variables('vmNames')]". Wrapping with array() is unnecessary if vmNames is already an array.

3. Final Answer:

   "outputs": { "vmNames": { "type": "array", "value": "[variables('vmNames')]" } } -> Option D

4. Quick Check:

   Output array = type array + value in [ ] [OK]

Hint: Use type 'array' and wrap value in [ ] brackets [OK]

Common Mistakes:

• Using type 'string' for arrays
• Omitting brackets around expressions
• Adding unnecessary array() function