Dynamic blocks vs for_each decision in Terraform - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to iterate over a collection of subnet CIDRs using for_each.

Terraform

resource "aws_subnet" "example" {
  for_each = [1]
  vpc_id     = var.vpc_id
  cidr_block = each.value
}

Drag options to blanks, or click blank then click option'

Aeach.value

Bvar.vpc_id

Caws_vpc.main

Dvar.subnet_cidrs

Attempts:

3 left

💡 Hint

Common Mistakes

Using a single value instead of a collection for for_each.

Confusing for_each with count.

The for_each argument expects a map or set of strings to iterate over. Here, var.subnet_cidrs is a collection of CIDR blocks for subnets.

2fill in blank

medium

Complete the dynamic block to add multiple ingress rules inside a security group.

Terraform

resource "aws_security_group" "example" {
  name        = "example-sg"
  description = "Example security group"

  dynamic "ingress" {
    for_each = [1]
    content {
      from_port   = ingress.value.from_port
      to_port     = ingress.value.to_port
      protocol    = ingress.value.protocol
      cidr_blocks = ingress.value.cidr_blocks
    }
  }
}

Drag options to blanks, or click blank then click option'

Avar.vpc_id

Bvar.ingress_rules

Caws_subnet.example

Dvar.subnet_cidrs

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning a non-collection value to for_each in dynamic block.

Using resource references instead of variables for rules.

The for_each inside a dynamic block should be assigned to a collection of ingress rule objects, here var.ingress_rules.

3fill in blank

hard

Fix the error in this dynamic block that tries to create multiple tags but uses incorrect syntax.

Terraform

resource "aws_instance" "example" {
  ami           = var.ami
  instance_type = var.instance_type

  dynamic "tag" {
    for_each = var.tags
    content {
      [1] = tag.key
      value       = tag.value
    }
  }
}

Drag options to blanks, or click blank then click option'

Akey

Btag_key

Ctags

Dtag

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'tags' instead of 'key' inside the content block.

Not providing both key and value attributes.

Inside a dynamic block for tags, the key should be key and the value should be value. Here, key = tag.key and value = tag.value is the correct pattern. The blank expects the key name, which is key.

4fill in blank

hard

Fill both blanks to correctly use for_each and dynamic block to create multiple EBS volumes attached to an instance.

Terraform

resource "aws_instance" "example" {
  ami           = var.ami
  instance_type = var.instance_type

  dynamic "ebs_block_device" {
    for_each = [1]
    content {
      device_name = ebs_block_device.value.device_name
      volume_size = [2]
    }
  }
}

Drag options to blanks, or click blank then click option'

Avar.ebs_volumes

Bvar.volume_sizes

Cebs_block_device.value.size

Debs_block_device.value.volume_size

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable that is not a collection for for_each.

Incorrect attribute name for volume size.

The for_each should iterate over var.ebs_volumes, which is a collection of volume objects. The volume size is accessed as ebs_block_device.value.volume_size inside the dynamic block.

5fill in blank

hard

Fill all three blanks to create multiple IAM policy statements using dynamic blocks with for_each.

Terraform

resource "aws_iam_role" "example" {
  name = "example-role"

  assume_role_policy = jsonencode({
    Version = "2012-10-17"
    Statement = [{
      Action = "sts:AssumeRole"
      Effect = "Allow"
      Principal = {
        Service = "ec2.amazonaws.com"
      }
    }]
  })
}

data "aws_iam_policy_document" "example" {
  dynamic "statement" {
    for_each = [1]
    content {
      effect    = "Allow"
      actions   = statement.value.[2]
      resources = statement.value.[3]
    }
  }
}

resource "aws_iam_role_policy" "example" {
  name   = "example-policy"
  role   = aws_iam_role.example.id
  policy = data.aws_iam_policy_document.example.json
}

Drag options to blanks, or click blank then click option'

Avar.policies

Bactions

Cresources

Dpolicy_name

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect keys for actions or resources.

Not using a map for for_each.

The for_each iterates over var.policies, a map of policy statements. The action and resource keys inside each policy are actions and resources respectively.

Practice

1. Which Terraform feature should you use to repeat a nested block inside a single resource?

easy

A. Dynamic blocks

B. for_each on the resource

C. count on the resource

D. locals block

Solution

1. Step 1: Understand nested block repetition

   Dynamic blocks are designed to repeat nested blocks inside a single resource.

2. Step 2: Compare with for_each usage

   for_each repeats entire resources or top-level blocks, not nested blocks.

3. Final Answer:

   Dynamic blocks -> Option A

4. Quick Check:

   Nested block repetition = Dynamic blocks [OK]

Hint: Use dynamic blocks for nested repeated settings [OK]

Common Mistakes:

• Using for_each to repeat nested blocks inside one resource
• Confusing count with dynamic blocks
• Trying to use locals for repeating blocks

2. Which syntax correctly uses a dynamic block inside a resource to repeat a nested block named setting?

easy

A. locals { setting = var.settings } resource { setting = local.setting }

B. for_each = var.settings { setting { key = each.value } }

C. count = length(var.settings) setting { key = var.settings[count.index] }

D. dynamic "setting" { for_each = var.settings; content { key = each.value } }

Solution

1. Step 1: Identify correct dynamic block syntax

   Dynamic blocks use the syntax: dynamic "block_name" { for_each = ... content { ... } }.

2. Step 2: Check other options for syntax errors

   Options A, B, and C misuse for_each, count, or locals incorrectly for nested blocks.

3. Final Answer:

   dynamic "setting" { for_each = var.settings; content { key = each.value } } -> Option D

4. Quick Check:

   Correct dynamic block syntax = dynamic "setting" { for_each = var.settings; content { key = each.value } } [OK]

Hint: Dynamic blocks use dynamic "name" with for_each and content [OK]

Common Mistakes:

• Placing for_each directly inside resource without dynamic
• Using count for nested blocks
• Trying to assign locals directly as blocks

3. Given this Terraform snippet, what will be the number of aws_security_group_rule resources created?

resource "aws_security_group_rule" "example" {
  for_each = { for idx, port in var.ports : idx => port }
  type        = "ingress"
  from_port   = each.value
  to_port     = each.value
  protocol    = "tcp"
  security_group_id = var.sg_id
}

Assuming var.ports = [80, 443].

medium

A. 1 resource

B. 2 resources

C. No resources, syntax error

D. One resource with two ports

Solution

1. Step 1: Understand for_each on resource

   for_each creates one resource instance per map or set element. Here, var.ports has 2 elements.

2. Step 2: Count resource instances

   Since var.ports has 2 ports, Terraform creates 2 aws_security_group_rule resources, one for each port.

3. Final Answer:

   2 resources -> Option B

4. Quick Check:

   for_each with 2 items = 2 resources [OK]

Hint: for_each creates one resource per item in collection [OK]

Common Mistakes:

• Thinking for_each creates one resource regardless of items
• Confusing dynamic blocks with resource repetition
• Assuming ports combine into one resource

4. This Terraform code throws an error. What is the main issue?

resource "aws_instance" "example" {
  for_each = var.instances
  ami           = "ami-123456"
  instance_type = "t2.micro"

  dynamic "ebs_block_device" {
    for_each = each.value.ebs_volumes
    content {
      device_name = ebs_block_device.value.device_name
      volume_size = ebs_block_device.value.size
    }
  }
}

Assuming var.instances is a map with nested ebs_volumes lists.

medium

A. Dynamic blocks cannot be nested inside resources

B. for_each cannot be used on resources

C. Incorrect reference to dynamic block variable inside content

D. Missing count argument on resource

Solution

1. Step 1: Identify the error in dynamic block reference

   Inside the content block of a dynamic block, the iterator must be referenced as each.value, not ebs_block_device.value. The iterator variable is always each regardless of the dynamic block name.

2. Step 2: Confirm the fix

   Change to device_name = each.value.device_name and volume_size = each.value.size. Other options are incorrect: dynamic blocks work inside resources, for_each works on resources, count is not required.

3. Final Answer:

   Incorrect reference to dynamic block variable inside content -> Option C

4. Quick Check:

   Dynamic block content uses each.value [OK]

Hint: Inside dynamic content, always use each.value, not block_name.value [OK]

Common Mistakes:

• Using block_name.value inside dynamic block content instead of each.value
• Trying to use for_each on resource incorrectly
• Forgetting to define for_each on dynamic block

5. You want to create multiple AWS IAM users, each with multiple inline policies. Which Terraform approach is best to manage this efficiently? A snippet of your variables:

variable "users" {
  type = map(object({
    policies = list(object({
      name   = string
      policy = string
    }))
  }))
}

hard

A. Use for_each on aws_iam_user for users, and for_each on aws_iam_user_policy for policies

B. Use count on aws_iam_user for users, and for_each on aws_iam_user_policy for policies

C. Use for_each on aws_iam_user resource for users, and dynamic blocks inside aws_iam_user_policy for policies

D. Use dynamic blocks on aws_iam_user resource for users, and count on aws_iam_user_policy for policies

Solution

1. Step 1: Manage multiple users

   Use for_each on aws_iam_user resource to create one user per map entry.

2. Step 2: Manage multiple policies per user

   Since policies are separate resources (aws_iam_user_policy), use for_each on that resource to create one policy per user-policy pair.

3. Step 3: Why not dynamic blocks here?

   Dynamic blocks repeat nested blocks inside a resource, but aws_iam_user_policy is a separate resource, so for_each is appropriate.

4. Final Answer:

   Use for_each on aws_iam_user for users, and for_each on aws_iam_user_policy for policies -> Option A

5. Quick Check:

   Multiple resources = for_each on both [OK]

Hint: Use for_each for multiple resources, dynamic blocks for nested blocks [OK]

Common Mistakes:

• Using dynamic blocks to create multiple resources
• Using count instead of for_each for maps
• Trying to nest policies inside user resource with dynamic blocks