Iterator variable in Terraform - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Configuration

intermediate

Terraform for_each with iterator variable

Given the following Terraform resource using for_each with an iterator variable, what will be the value of the tags attribute for the resource named server2?

Terraform

variable "servers" {
  default = {
    server1 = "10.0.0.1"
    server2 = "10.0.0.2"
    server3 = "10.0.0.3"
  }
}

resource "aws_instance" "example" {
  for_each = var.servers

  ami           = "ami-123456"
  instance_type = "t2.micro"

  tags = {
    Name = each.key
    IP   = each.value
  }
}

A {"Name" = "server2", "IP" = "10.0.0.2"}

B {"Name" = "server3", "IP" = "10.0.0.3"}

C {"Name" = "server1", "IP" = "10.0.0.1"}

D {"Name" = "server2", "IP" = "10.0.0.3"}

💡 Hint

Remember that each.key is the map key and each.value is the map value in for_each.

The for_each iterates over the map variable servers. For the resource named server2, each.key is "server2" and each.value is "10.0.0.2". So the tags reflect these values.

❓ service_behavior

intermediate

Effect of iterator variable in dynamic block

In Terraform, what will be the number of ingress rules created by the following security group resource?

Terraform

variable "ports" {
  default = [22, 80, 443]
}

resource "aws_security_group" "example" {
  name = "example-sg"

  dynamic "ingress" {
    for_each = var.ports
    content {
      from_port   = ingress.value
      to_port     = ingress.value
      protocol    = "tcp"
      cidr_blocks = ["0.0.0.0/0"]
    }
  }
}

A 3

B 1

C Error: dynamic block requires a map, not a list

D 0

💡 Hint

Dynamic blocks can iterate over lists or maps to create multiple nested blocks.

The dynamic block iterates over the list of ports [22, 80, 443], creating one ingress block per port, so 3 ingress rules are created.

❓ Architecture

advanced

Using iterator variable in module instantiation

You have a Terraform module that creates a virtual machine. You want to instantiate this module multiple times with different names and IPs using an iterator variable. Which of the following for_each expressions correctly uses the iterator variable to assign unique names and IPs inside the module?

Terraform

variable "vm_configs" {
  default = {
    vm1 = "192.168.1.10"
    vm2 = "192.168.1.11"
  }
}

module "vms" {
  source = "./vm_module"

  for_each = var.vm_configs

  name = ???
  ip   = ???
}

A

name = each
ip = each

B

name = each.value
ip = each.key

C

name = vm_configs.key
ip = vm_configs.value

D

name = each.key
ip = each.value

💡 Hint

Inside a for_each block, each.key and each.value refer to the current map key and value.

The for_each iterates over the map vm_configs. each.key is the VM name and each.value is the IP address. So assigning name = each.key and ip = each.value correctly passes unique values to each module instance.

❓ security

advanced

Iterator variable misuse causing security risk

Consider this Terraform snippet for creating multiple IAM users with policies. What is the security risk caused by incorrect use of the iterator variable?

Terraform

variable "users" {
  default = ["alice", "bob"]
}

resource "aws_iam_user" "users" {
  for_each = toset(var.users)
  name     = each.value
}

resource "aws_iam_policy_attachment" "attach" {
  for_each = toset(var.users)
  name       = "attach-${each.value}"
  users      = [aws_iam_user.users[each.key].name]
  policy_arn = "arn:aws:iam::aws:policy/ReadOnlyAccess"
}

A The IAM users are created with duplicate names causing overwrite.

B The policy attachment correctly references users by each.value, no risk present.

C The policy attachment references aws_iam_user with each.key, which is invalid and causes a runtime error.

D The policy ARN is incorrect, causing no policy to attach.

💡 Hint

Check how the keys and values are used in the for_each maps and sets.

The for_each uses a set, so each.key is the user name string, not an index. Using aws_iam_user.users[each.key] is invalid because the resource keys are user names, but the code uses each.key as an index. This causes a runtime error and no policy attachment.

✅ Best Practice

expert

Correct use of iterator variable in nested for_each

You want to create multiple AWS S3 buckets, each with multiple lifecycle rules. Which option correctly uses nested for_each with iterator variables to assign lifecycle rules to each bucket?

Terraform

variable "buckets" {
  default = {
    bucket1 = ["logs", "archive"]
    bucket2 = ["temp", "backup"]
  }
}

resource "aws_s3_bucket" "buckets" {
  for_each = var.buckets
  bucket   = each.key

  lifecycle_rule {
    for_each = ???
    id      = ???
    enabled = true
    prefix  = "${each.value}-"
    tags = {
      rule = each.key
    }
  }
}

A

for_each = each.key
id = each.value

B

for_each = toset(each.value)
id = each.value

C

for_each = toset(each.value)
id = each.key

D

for_each = each.value
id = each.key

💡 Hint

The outer each refers to buckets, the inner each refers to lifecycle rules.

The outer each.value is a list of lifecycle rule names. Converting it to a set with toset(each.value) allows iteration. The inner each.value is the rule name, so id = each.value uniquely identifies each lifecycle rule.