Nested dynamic blocks in Terraform - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a nested dynamic block in Terraform?

A nested dynamic block is a dynamic block placed inside another dynamic block, allowing you to generate complex, repeated nested configurations based on input data.

beginner

Why use nested dynamic blocks instead of static blocks?

Nested dynamic blocks let you create flexible, reusable infrastructure code that adapts to varying input sizes and structures without manually writing repetitive blocks.

beginner

In Terraform, what keyword is used to define a dynamic block?

The keyword dynamic is used to define a dynamic block, which generates nested blocks based on a for_each expression.

intermediate

How do you access the inner block's content inside a nested dynamic block?

Inside a nested dynamic block, you use content to define the inner block's attributes, and you can reference the current item with each.value or each.key.

intermediate

What is a common use case for nested dynamic blocks in Terraform?

A common use case is defining complex resources like security groups with multiple rules, where each rule has multiple nested attributes like ports and protocols.

What does a nested dynamic block in Terraform allow you to do?

A Generate repeated nested blocks based on input data

B Create static blocks only

C Run Terraform commands automatically

D Define variables outside modules

Nested dynamic blocks generate repeated nested blocks dynamically based on input data.

Which keyword starts a dynamic block in Terraform?

A dynamic

B block

C repeat

D for_each

The keyword 'dynamic' is used to define dynamic blocks.

How do you reference the current item inside a dynamic block?

A item.value

B current.value

C each.value

D this.value

Inside dynamic blocks, 'each.value' references the current item.

What is the purpose of the 'content' block inside a dynamic block?

A Imports modules

B Runs Terraform apply

C Declares variables

D Defines the nested block's attributes

'content' defines the attributes of the nested block generated by the dynamic block.

Which scenario best fits using nested dynamic blocks?

A Running Terraform plan

B Creating multiple nested firewall rules with varying ports

C Defining a single static resource

D Setting environment variables

Nested dynamic blocks are ideal for complex nested configurations like multiple firewall rules.

Explain how nested dynamic blocks work in Terraform and why they are useful.

Think about how you can repeat blocks inside other repeated blocks.

Describe a real-world example where nested dynamic blocks would simplify Terraform code.

Consider network security settings with many detailed rules.

Practice

1.

What is the main purpose of using nested dynamic blocks in Terraform?

easy

A. To write static configuration without loops

B. To create repeated blocks inside other repeated blocks dynamically

C. To define provider settings only

D. To manage Terraform state files

Solution

1. Step 1: Understand dynamic blocks

   Dynamic blocks allow repeating a block multiple times based on a list or map.

2. Step 2: Understand nested dynamic blocks

   Nested dynamic blocks repeat blocks inside other repeated blocks, useful for complex nested lists.

3. Final Answer:

   To create repeated blocks inside other repeated blocks dynamically -> Option B

4. Quick Check:

   Nested dynamic blocks = repeated blocks inside repeated blocks [OK]

Hint: Think of loops inside loops for nested resources [OK]

Common Mistakes:

• Confusing dynamic blocks with static blocks
• Using nested dynamic blocks for simple flat lists
• Thinking dynamic blocks manage state files

2.

Which of the following is the correct syntax to start a nested dynamic block named subnet inside a dynamic block named network?

dynamic "network" {
  for_each = var.networks
  content {
    name = network.value.name
    // What goes here?
  }
}

easy

A. dynamic "subnet" { for_each = network.value.subnets content { cidr_block = subnet.value } }

B. dynamic subnet { for_each = network.value.subnets content { cidr_block = subnet.value } }

C. dynamic "subnet" for_each = network.value.subnets { content { cidr_block = subnet.value } }

D. dynamic "subnet" { for_each = var.subnets content { cidr_block = subnet.value } }

Solution

1. Step 1: Identify correct dynamic block syntax

   Dynamic blocks require the keyword dynamic, block name in quotes, then for_each and content blocks.

2. Step 2: Check nested dynamic block context

   Inside the network dynamic block, use network.value.subnets for for_each and define content with subnet.value.

3. Final Answer:

   dynamic "subnet" { for_each = network.value.subnets content { cidr_block = subnet.value } } -> Option A

4. Quick Check:

   Correct syntax uses quotes and nested for_each [OK]

Hint: Remember dynamic block name must be in quotes [OK]

Common Mistakes:

• Omitting quotes around block name
• Using wrong variable for for_each
• Placing for_each outside the braces

3.

Given the following Terraform snippet, what will be the value of resource.aws_vpc.example tags after deployment?

variable "vpcs" {
  default = [
    { name = "vpc1", tags = ["tag1", "tag2"] },
    { name = "vpc2", tags = ["tag3"] }
  ]
}

resource "aws_vpc" "example" {
  for_each = { for v in var.vpcs : v.name => v }
  cidr_block = "10.0.0.0/16"

  dynamic "tags" {
    for_each = each.value.tags
    content {
      key   = tags.value
      value = "true"
    }
  }
}

medium

A. Tags will be empty because tags block is not supported inside aws_vpc

B. {"tags" = ["tag1", "tag2"]} for vpc1 and {"tags" = ["tag3"]} for vpc2

C. No tags will be created because dynamic blocks cannot be nested

D. {"tag1" = "true", "tag2" = "true"} for vpc1 and {"tag3" = "true"} for vpc2

Solution

1. Step 1: Understand for_each on resource

   Resource creates two VPCs named vpc1 and vpc2 with their respective tags list.

2. Step 2: Analyze nested dynamic block for tags

   Dynamic block iterates over each.value.tags, creating a tag key with value "true" for each tag string.

3. Final Answer:

   {"tag1" = "true", "tag2" = "true"} for vpc1 and {"tag3" = "true"} for vpc2 -> Option D

4. Quick Check:

   Dynamic tags create key-value pairs from list items [OK]

Hint: Dynamic blocks create repeated nested blocks from lists [OK]

Common Mistakes:

• Assuming tags remain as list instead of key-value map
• Thinking dynamic blocks cannot be nested
• Ignoring the for_each on resource

4.

Identify the error in this nested dynamic block snippet:

dynamic "network" {
  for_each = var.networks
  content {
    name = network.value.name
    dynamic "subnet" {
      for_each = var.subnets
      content {
        cidr_block = subnet.value.cidr
      }
    }
  }
}

medium

A. Incorrect use of content block inside dynamic

B. Missing quotes around subnet in dynamic block

C. Using var.subnets instead of network.value.subnets for nested for_each

D. network.value.name is invalid syntax

Solution

1. Step 1: Check nested for_each source

   The nested dynamic block should iterate over subnets related to the current network, not the entire var.subnets list.

2. Step 2: Confirm correct variable usage

   Using var.subnets ignores the current network context; it should be network.value.subnets to nest properly.

3. Final Answer:

   Using var.subnets instead of network.value.subnets for nested for_each -> Option C

4. Quick Check:

   Nested for_each must use parent block's value [OK]

Hint: Nested loops must use parent block's current item [OK]

Common Mistakes:

• Using global variables instead of nested context
• Forgetting quotes around dynamic block names
• Misplacing content blocks

5.

You have a variable var.services which is a list of maps. Each map has a name and a list of ports. You want to create an aws_security_group resource with nested dynamic blocks to create ingress rules for each port of each service. Which Terraform code snippet correctly implements this?

hard

A. resource "aws_security_group" "example" {
for_each = { for s in var.services : s.name => s }
name = each.key

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

B. resource "aws_security_group" "example" {
for_each = var.services
name = each.value.name

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

C. resource "aws_security_group" "example" {
for_each = { for s in var.services : s.name => s }
name = each.key

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

D. resource "aws_security_group" "example" {
for_each = { for s in var.services : s.name => s }
name = each.key

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

Solution

1. Step 1: Use for_each on resource with map keyed by service name

   This allows referencing each service by name with each.key and each.value.

2. Step 2: Use nested dynamic block for ingress rules

   Dynamic block named "ingress" iterates over each.value.ports with for_each and uses ingress.value for port numbers.

3. Final Answer:

   Code snippet in Option A correctly uses nested dynamic blocks with proper variable references -> Option A

4. Quick Check:

   Nested dynamic blocks need correct for_each and value references [OK]

Hint: Use each.value and ingress.value inside nested dynamic blocks [OK]

Common Mistakes:

• Omitting quotes around dynamic block name
• Using wrong variable names like ports.value instead of ingress.value
• Not using map for resource for_each