Splat expressions in Terraform - Mini Project: Build & Apply

Using Splat Expressions in Terraform

📖 Scenario: You are managing cloud infrastructure using Terraform. You have multiple virtual machines (VMs) defined, and you want to collect their public IP addresses easily.

🎯 Goal: Create a Terraform configuration that defines three virtual machines with specific names and public IPs. Then, use a splat expression to extract all their public IP addresses into a list variable.

📋 What You'll Learn

Define a list variable vm_names with three VM names: "vm1", "vm2", "vm3"

Create three aws_instance resources using a for_each loop over vm_names

Each instance must have a public_ip attribute set to a unique IP string

Use a splat expression to create a list variable public_ips containing all public IPs from the instances

💡 Why This Matters

🌍 Real World

Splat expressions help you gather information from multiple cloud resources easily, such as collecting all IP addresses or IDs for further use.

💼 Career

Cloud engineers often need to manage many resources and extract their attributes efficiently; splat expressions simplify this process in Terraform.

1

Define the VM names list variable

Create a Terraform variable called vm_names as a list with these exact values: "vm1", "vm2", "vm3".

Terraform

# Define the vm_names variable as a list of three VM names
# Your code here

Need a hint?

Use variable "vm_names" with type = list(string) and set default to the list of names.

2

Create aws_instance resources using for_each

Create aws_instance resources named example using for_each over var.vm_names. Set the public_ip attribute to "10.0.0.${index(toset(var.vm_names), each.key) + 1}" for each instance.

Terraform

variable "vm_names" {
  type    = list(string)
  default = ["vm1", "vm2", "vm3"]
}

# Create aws_instance resources with for_each over var.vm_names
# Your code here

Need a hint?

Use for_each = toset(var.vm_names) and set public_ip using the index of each key plus 1.

3

Use a splat expression to get all public IPs

Create a local variable called public_ips that uses a splat expression to collect all public_ip values from aws_instance.example resources.

Terraform

variable "vm_names" {
  type    = list(string)
  default = ["vm1", "vm2", "vm3"]
}

resource "aws_instance" "example" {
  for_each = toset(var.vm_names)

  ami           = "ami-12345678"
  instance_type = "t2.micro"
  associate_public_ip_address = true
  public_ip     = "10.0.0.${index(toset(var.vm_names), each.key) + 1}"
}

# Create local variable public_ips using splat expression
# Your code here

Need a hint?

Use locals block and assign public_ips = aws_instance.example[*].public_ip.

4

Output the list of public IPs

Add an output block named all_public_ips that outputs the local variable public_ips.

Terraform

variable "vm_names" {
  type    = list(string)
  default = ["vm1", "vm2", "vm3"]
}

resource "aws_instance" "example" {
  for_each = toset(var.vm_names)

  ami           = "ami-12345678"
  instance_type = "t2.micro"
  associate_public_ip_address = true
  public_ip     = "10.0.0.${index(toset(var.vm_names), each.key) + 1}"
}

locals {
  public_ips = aws_instance.example[*].public_ip
}

# Add output block all_public_ips to output local.public_ips
# Your code here

Need a hint?

Use output "all_public_ips" block with value = local.public_ips.