Nested dynamic blocks in Terraform - Mini Project: Build & Apply

Nested dynamic blocks

📖 Scenario: You are setting up a cloud infrastructure using Terraform. You need to create a resource that has nested blocks which are generated dynamically based on input variables. This is common when configuring complex cloud resources like load balancers or security groups.

🎯 Goal: Build a Terraform configuration that uses nested dynamic blocks to create multiple nested blocks inside a resource. You will first define the data structure, then create the dynamic blocks for the inner and outer levels.

📋 What You'll Learn

Create a variable listeners with a list of maps, each map containing port and protocol keys

Create a variable rules with a list of maps, each map containing host and paths keys, where paths is a list of strings

Use a dynamic block named listener to iterate over listeners

Inside each listener block, use a nested dynamic block named rule to iterate over rules

Inside each rule block, use a nested dynamic block named path to iterate over the paths list

💡 Why This Matters

🌍 Real World

Cloud engineers often need to configure resources with multiple nested settings that vary by environment or input. Nested dynamic blocks let them write flexible, reusable Terraform code.

💼 Career

Understanding nested dynamic blocks is essential for Terraform users working in cloud infrastructure roles, enabling them to automate complex resource setups efficiently.

1

Define the listeners variable

Create a Terraform variable called listeners of type list with two maps. The first map should have port = 80 and protocol = "HTTP". The second map should have port = 443 and protocol = "HTTPS".

Terraform

# Define the variable listeners with two maps
# Your code here

Need a hint?

Use variable "listeners" with type = list(object({ port = number, protocol = string })) and set the default to the two maps.

2

Define the rules variable with nested paths

Create a Terraform variable called rules of type list with two maps. The first map should have host = "example.com" and paths = ["/", "/app"]. The second map should have host = "test.com" and paths = ["/test"].

Terraform

variable "listeners" {
  type = list(object({
    port     = number
    protocol = string
  }))
  default = [
    { port = 80, protocol = "HTTP" },
    { port = 443, protocol = "HTTPS" }
  ]
}

# Define the variable rules with two maps including paths
# Your code here

Need a hint?

Use variable "rules" with type = list(object({ host = string, paths = list(string) })) and set the default to the two maps.

3

Create the outer dynamic "listener" block

Inside a resource aws_lb named example, add a dynamic "listener" block that iterates over var.listeners. For each listener, set port and protocol attributes using listener.value.port and listener.value.protocol.

Terraform

variable "listeners" {
  type = list(object({
    port     = number
    protocol = string
  }))
  default = [
    { port = 80, protocol = "HTTP" },
    { port = 443, protocol = "HTTPS" }
  ]
}

variable "rules" {
  type = list(object({
    host  = string
    paths = list(string)
  }))
  default = [
    { host = "example.com", paths = ["/", "/app"] },
    { host = "test.com", paths = ["/test"] }
  ]
}

resource "aws_lb" "example" {
  name               = "example-lb"
  internal           = false
  load_balancer_type = "application"
  subnets            = ["subnet-12345", "subnet-67890"]

  # Add a dynamic block named listener iterating over var.listeners
  # Your code here
}

Need a hint?

Use dynamic "listener" with for_each = var.listeners and set port and protocol inside content.

4

Add nested dynamic "rule" and dynamic "path" blocks inside listener

Inside the content block of the dynamic "listener", add a nested dynamic "rule" block that iterates over var.rules. Inside each rule block, set host to rule.value.host. Then add a nested dynamic "path" block inside rule that iterates over rule.value.paths. Inside path, set value to path.value.

Terraform

variable "listeners" {
  type = list(object({
    port     = number
    protocol = string
  }))
  default = [
    { port = 80, protocol = "HTTP" },
    { port = 443, protocol = "HTTPS" }
  ]
}

variable "rules" {
  type = list(object({
    host  = string
    paths = list(string)
  }))
  default = [
    { host = "example.com", paths = ["/", "/app"] },
    { host = "test.com", paths = ["/test"] }
  ]
}

resource "aws_lb" "example" {
  name               = "example-lb"
  internal           = false
  load_balancer_type = "application"
  subnets            = ["subnet-12345", "subnet-67890"]

  dynamic "listener" {
    for_each = var.listeners
    content {
      port     = listener.value.port
      protocol = listener.value.protocol

      # Add a nested dynamic block named rule iterating over var.rules
      # Inside rule, set host to rule.value.host
      # Inside rule, add a nested dynamic block named path iterating over rule.value.paths
      # Inside path, set value to path.value
      # Your code here
    }
  }
}

Need a hint?

Inside listener content, add dynamic "rule" with for_each = var.rules. Inside rule content, set host = rule.value.host and add dynamic "path" with for_each = rule.value.paths. Inside path content, set value = path.value.