Iterator variable in Terraform - Mini Project: Build & Apply

Iterator Variable in Terraform

📖 Scenario: You are setting up a simple cloud infrastructure using Terraform. You want to create multiple virtual machines (VMs) with specific names and sizes.

🎯 Goal: Build a Terraform configuration that uses an iterator variable to create multiple VMs with different names and sizes.

📋 What You'll Learn

Create a variable called vm_specs as a list of maps with exact entries

Create a local variable called vm_names that extracts VM names from vm_specs

Use a for expression with an iterator variable spec to create a map of VM sizes keyed by VM names

Define a resource azurerm_virtual_machine using the iterator variable spec in a for_each block

💡 Why This Matters

🌍 Real World

This project shows how to use iterator variables in Terraform to manage multiple cloud resources efficiently.

💼 Career

Understanding iterator variables is essential for cloud engineers to write scalable and maintainable infrastructure code.

1

Create the VM specifications variable

Create a Terraform variable called vm_specs as a list of maps with these exact entries: { name = "vm1", size = "Standard_B1s" }, { name = "vm2", size = "Standard_B2s" }, and { name = "vm3", size = "Standard_B1ms" }.

Terraform

# Your code here

Hint

Define a variable with type list of objects containing name and size keys.

2

Create a local variable for VM names

Create a local variable called vm_names that extracts the name from each element in the var.vm_specs list using a for expression with iterator variable spec.

Terraform

variable "vm_specs" {
  type = list(object({
    name = string
    size = string
  }))
  default = [
    { name = "vm1", size = "Standard_B1s" },
    { name = "vm2", size = "Standard_B2s" },
    { name = "vm3", size = "Standard_B1ms" }
  ]
}

# Your code here

Hint

Use a for expression with spec as iterator to get names.

3

Create a map of VM sizes keyed by VM names

Create a local variable called vm_sizes_map that uses a for expression with iterator variable spec over var.vm_specs to create a map where keys are spec.name and values are spec.size.

Terraform

variable "vm_specs" {
  type = list(object({
    name = string
    size = string
  }))
  default = [
    { name = "vm1", size = "Standard_B1s" },
    { name = "vm2", size = "Standard_B2s" },
    { name = "vm3", size = "Standard_B1ms" }
  ]
}

locals {
  vm_names = [for spec in var.vm_specs : spec.name]
  # Your code here
}

Hint

Use a for expression with spec to build a map of names to sizes.

4

Define VM resources using the iterator variable

Define a resource block resource "azurerm_virtual_machine" "example" that uses for_each = { for spec in var.vm_specs : spec.name => spec }. Inside the resource, set name = each.key and vm_size = each.value.size to use the iterator variable spec indirectly via each.

Terraform

variable "vm_specs" {
  type = list(object({
    name = string
    size = string
  }))
  default = [
    { name = "vm1", size = "Standard_B1s" },
    { name = "vm2", size = "Standard_B2s" },
    { name = "vm3", size = "Standard_B1ms" }
  ]
}

locals {
  vm_names = [for spec in var.vm_specs : spec.name]
  vm_sizes_map = { for spec in var.vm_specs : spec.name => spec.size }
}

# Your code here

Hint

Use for_each with a map from spec.name to spec. Use each.key and each.value.size inside the resource.

Practice

1. What is the role of an iterator variable in a Terraform for expression?

easy

A. It represents each item in the list or map during iteration.

B. It defines the output type of the expression.

C. It sets the maximum number of iterations.

D. It stores the final result of the iteration.

Solution

1. Step 1: Understand the iterator variable concept

   The iterator variable is a placeholder that takes each value from the list or map one by one during the loop.

2. Step 2: Identify its role in the for expression

   It allows Terraform to perform actions on each item individually, making the code reusable and clean.

3. Final Answer:

   It represents each item in the list or map during iteration. -> Option A

4. Quick Check:

   Iterator variable = item placeholder [OK]

Hint: Think of iterator as the 'current item' in a loop [OK]

Common Mistakes:

• Confusing iterator with output variable
• Assuming iterator sets iteration count
• Thinking iterator stores final results

2. Which of the following is the correct syntax for using an iterator variable item in a Terraform for expression over a list var.names?

easy

A. for item in var.names : item

B. [for item var.names : item]

C. [for item in var.names : item]

D. for (item in var.names) { item }

Solution

1. Step 1: Recall Terraform for expression syntax

   Terraform uses square brackets with for item in list : expression to create a new list.

2. Step 2: Match the correct syntax

   [for item in var.names : item] matches the correct syntax: [for item in var.names : item].

3. Final Answer:

   [for item in var.names : item] -> Option C

4. Quick Check:

   Correct for expression syntax = [for item in var.names : item] [OK]

Hint: Remember: Terraform for expressions use square brackets [OK]

Common Mistakes:

• Omitting square brackets
• Using parentheses instead of brackets
• Missing 'in' keyword

3. Given the Terraform expression:

[for num in [1, 2, 3] : num * 2]

What is the resulting list?

medium

A. [1, 2, 3]

B. [2, 4, 6]

C. [3, 4, 5]

D. [2, 3, 4]

Solution

1. Step 1: Identify the iterator and list

   The iterator variable is num, iterating over the list [1, 2, 3].

2. Step 2: Calculate each iteration's output

   Each num is multiplied by 2: 1*2=2, 2*2=4, 3*2=6.

3. Final Answer:

   [2, 4, 6] -> Option B

4. Quick Check:

   Multiply each item by 2 = [2, 4, 6] [OK]

Hint: Apply the operation to each item in the list [OK]

Common Mistakes:

• Confusing multiplication with addition
• Returning original list without changes
• Misreading the iterator variable

4. Identify the error in this Terraform for expression:

[for i var.list : i * 3]

medium

A. Missing 'in' keyword between iterator and list.

B. Iterator variable should be a string, not 'i'.

C. Square brackets are not allowed around for expressions.

D. The multiplication operator '*' is invalid here.

Solution

1. Step 1: Check for correct for expression syntax

   The correct syntax requires the keyword 'in' between the iterator and the list.

2. Step 2: Identify the missing keyword

   The expression misses 'in' after 'i', causing a syntax error.

3. Final Answer:

   Missing 'in' keyword between iterator and list. -> Option A

4. Quick Check:

   For expressions need 'in' keyword [OK]

Hint: Always include 'in' between iterator and collection [OK]

Common Mistakes:

• Forgetting 'in' keyword
• Using wrong brackets
• Misplacing operators

5. You want to create a map from a list of server names var.servers = ["web", "db", "cache"] where each key is the server name and the value is the server port starting at 8000 incremented by 1. Which Terraform expression correctly uses an iterator variable to achieve this?

hard

A. { for srv in var.servers : srv => 8000 }

B. { for srv in var.servers : 8000 => srv }

C. [for srv in var.servers : { srv = 8000 }]

D. { for idx, srv in var.servers : srv => 8000 + idx }

Solution

1. Step 1: Understand the requirement

   Create a map where keys are server names and values are ports starting at 8000 incremented by 1.

2. Step 2: Analyze options for correct iterator usage

   { for idx, srv in var.servers : srv => 8000 + idx } uses for idx, srv in var.servers to get index and server name, then maps srv => 8000 + idx, correctly incrementing ports.

3. Final Answer:

   { for idx, srv in var.servers : srv => 8000 + idx } -> Option D

4. Quick Check:

   Use index and value in for map expression [OK]

Hint: Use index and value in for map to increment ports [OK]

Common Mistakes:

• Using list syntax instead of map
• Not using index to increment port
• Swapping key and value positions