ARM template parameters and variables in Azure - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of parameters in an ARM template?

Parameters allow you to pass values into the ARM template when deploying. They make the template flexible and reusable by letting you customize settings without changing the template code.

beginner

What are variables used for in an ARM template?

Variables store values that you want to reuse inside the template. They help avoid repeating the same value multiple times and can hold expressions or calculated values.

intermediate

Can you change the value of a variable during deployment in an ARM template?

No, variables are fixed once the template starts deploying. They are evaluated at deployment time but cannot be changed dynamically during deployment.

beginner

How do parameters improve the reusability of ARM templates?

By using parameters, you can deploy the same template with different values for each deployment, like different names or sizes, without editing the template itself.

intermediate

Give an example of when to use a variable instead of a parameter in an ARM template.

Use a variable when you want to create a value based on parameters or other variables, like combining a resource name prefix with a unique ID, so you don’t have to pass it every time.

What is the main difference between parameters and variables in an ARM template?

A Both are used to accept input during deployment.

B Variables accept input during deployment; parameters are set inside the template.

C Parameters accept input during deployment; variables are set inside the template.

D Both are fixed and cannot be changed.

Parameters accept input values when deploying the template, while variables are defined inside the template and cannot be changed during deployment.

Which ARM template element would you use to store a calculated value used multiple times?

A Output

B Parameter

C Resource

D Variable

Variables store calculated or repeated values inside the template for reuse.

Can you change a parameter value after deployment starts?

A No, parameters are fixed once deployment starts.

B Only for variables, not parameters.

C Only if you redeploy the template.

D Yes, anytime during deployment.

Parameters are set at deployment start and cannot be changed during deployment.

Why use parameters in ARM templates?

A To hardcode values inside the template.

B To allow customization without editing the template.

C To store temporary values during deployment.

D To output deployment results.

Parameters let you customize deployments by passing different values without changing the template.

Which of these is NOT a valid use of variables in ARM templates?

A Accepting user input during deployment.

B Holding a repeated value used multiple times.

C Storing a resource name built from parameters.

D Calculating a value based on other variables.

Variables cannot accept user input; only parameters do.

Explain the roles of parameters and variables in an ARM template and how they help in deployment.

Think about what you can change when you deploy versus what is fixed inside the template.

Describe a scenario where using a variable in an ARM template is better than using a parameter.

Consider when you want to create a value from other values instead of asking the user to provide it.

Practice

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