ARM template outputs in Azure - Step-by-Step Execution

Process Flow - ARM template outputs

Define Outputs Section

↓

Reference Resource Properties

↓

Assign Output Values

↓

Deploy Template

↓

Retrieve Outputs

↓

Use Outputs in Scripts or UI

This flow shows how outputs are defined in an ARM template, assigned values from resources, deployed, and then retrieved for use.

Execution Sample

Azure

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

Defines an output named storageAccountName that returns the storage account name variable after deployment.

Process Table

Step	Action	Evaluation	Result
1	Define outputs section in template	Outputs section with storageAccountName key	Outputs section ready
2	Assign value to output	Value set to variable 'storageAccountName'	Output storageAccountName = 'mystorageacct123'
3	Deploy ARM template	Template deploys resources and outputs	Resources created, outputs stored
4	Retrieve outputs after deployment	Query outputs from deployment result	storageAccountName = 'mystorageacct123'
5	Use output in script or UI	Reference output value	Output value used successfully
6	End	No more outputs to retrieve	Execution complete

💡 All outputs retrieved and deployment finished

Status Tracker

Variable	Start	After 1	After 2	Final
storageAccountName	undefined	mystorageacct123	mystorageacct123	mystorageacct123

Key Moments - 3 Insights

Why do outputs need a type like 'string' or 'object'?

Outputs require a type to tell Azure how to handle and display the value, as shown in step 2 of the execution_table where the output type is 'string'.

Can outputs reference resources created in the same template?

Yes, outputs often reference resource properties created during deployment, as in step 2 where the output value uses a variable linked to a resource.

When can you access the output values?

Outputs are accessible only after deployment completes successfully, as shown in step 4 where outputs are retrieved.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output value of 'storageAccountName' at step 2?

A "storageAccountName"

B "undefined"

C "mystorageacct123"

D "variables('storageAccountName')"

💡 Hint

Check the 'Result' column in row 2 of the execution_table.

At which step does the ARM template deployment complete and outputs become available?

A Step 4

B Step 3

C Step 5

D Step 2

💡 Hint

Look for when outputs are retrieved in the execution_table.

If the output type was missing, what would happen during deployment?

A Output is ignored silently

B Deployment fails due to missing output type

C Output defaults to string type

D Deployment succeeds but output is unusable

💡 Hint

Refer to key_moments about output type importance.

Concept Snapshot

ARM template outputs let you return values after deployment.
Define outputs in the 'outputs' section with a name, type, and value.
Values often reference resource properties or variables.
Outputs are accessible only after deployment finishes.
Use outputs to pass info to scripts or other templates.

Full Transcript

ARM template outputs are defined in the outputs section of the template JSON. Each output has a name, a type like string or object, and a value that usually references a resource property or variable. When you deploy the template, Azure creates the resources and stores the output values. After deployment completes, you can retrieve these outputs to use in scripts, UI, or other templates. Outputs must have a type to be valid. This flow ensures you get important info like resource names or IDs after deployment.

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