Demo Variables

Welcome to this hands-on lab on defining and using variables in Terraform (OpenTofu). By the end of this tutorial, you’ll understand how to declare different variable types, fetch elements from maps and lists, and refactor resources to leverage variables for cleaner, reusable configurations.

1. Variable Type Quiz

Question: Which of the following is not a valid Terraform variable type?

• object
• item
• tuple
• list
• map

Answer: item is not a valid variable type in Terraform/OpenTofu.

For more details, see the Terraform Variable Types.

2. Data Type Quiz

Question: Which of the following is not a valid data type in OpenTofu?

• list
• tuple
• map
• array
• set

Answer: array is not a valid data type in OpenTofu.

Setup: Navigate to the Variables Directory

cd /root/OpenTofu-project/variables

3. Inspecting number

Open variables.tf and locate:

variable "number" {
  type    = bool
  default = false
}

Question: Which type does number belong to?
Answer: It’s a boolean.

4. Fetching a Map Value

In variables.tf, you have:

variable "hard_drive" {
  type = map(string)
  default = {
    slow = "HDD"
    fast = "SSD"
  }
}

Question: How do you retrieve the "slow" entry?

var.hard_drive["slow"]

5. List Indexing

Definition in variables.tf:

variable "gender" {
  type    = list(string)
  default = ["Male", "Female"]
}

• Lists are zero-indexed.
• "Male" → index 0
• "Female" → index 1

Answer: The index of "Female" is 1.

6. Identifying a Set Definition Error

variable "users" {
  type    = set(string)
  default = ["tom", "jerry", "pluto", "daffy", "donald", "jerry"]
}

• Type: set(string)
• Mistake: Sets must not contain duplicates; "jerry" appears twice.

7. Inspecting a Resource Block

In main.tf, you added:

resource "local_file" "jedi" {
  filename = "/root/first-jedi"
  content  = "phanius"
}

Question: What is the value of the content argument?
Answer: "phanius"

8. Refactoring to Use Variables

1. Declare a map variable in variables.tf:

   variable "jedi" {
     type = map(string)
     default = {
       filename = "/root/first-jedi"
       content  = "phanius"
     }
   }
   

2. Update the resource in main.tf:

   resource "local_file" "jedi" {
     filename = var.jedi["filename"]
     content  = var.jedi["content"]
   }
   

This makes your configuration more modular and easier to maintain.

9. Initialize, Plan, and Apply

cd /root/OpenTofu-project/variables
opentofu init
opentofu plan

Expected output snapshot:

+ resource "local_file" "jedi" {
    + content     = "phanius"
    + filename    = "/root/first-jedi"
    ...
  }

Plan: 1 to add, 0 to change, 0 to destroy.

Apply the changes:

opentofu apply
# Confirm with "yes"

After success:

local_file.jedi: Creating...
local_file.jedi: Creation complete after 0s [id=...]
Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

Verify the file:

cat /root/first-jedi
# phanius

That’s it for this lab. Thank you for following along!

Links and References

• Terraform Variables Documentation
• OpenTofu GitHub Repository
• Terraform Local Provider