Devops

Day 63 - Mastering Terraform Variables

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Dhruv Moradiya
·

4 min read

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Terraform variables are essential for managing infrastructure-as-code efficiently. They allow flexibility, reusability, and modularity, especially when handling values such as instance names, configurations, file paths, or any other inputs. This blog explores variables in Terraform, their types, and practical applications, guiding you step-by-step through tasks to enhance your hands-on skills.

What Are Variables in Terraform?

Variables in Terraform act as placeholders for dynamic values in configuration files. Instead of hardcoding values, you define variables that can be used throughout your Terraform scripts. This simplifies updates and scales your infrastructure more effectively.

How to Use Terraform Variables

  1. Define variables in a separate file (variables.tf):
    Keep all your variable definitions in one place for better readability and manageability.

  2. Access variables using the var object:
    In your main.tf file or other resources, reference variables using var.<variable_name>.

Implementation

Let’s dive into two key tasks that will demonstrate Terraform variables.

Task 1: Create a Local File Using Terraform

Step 1: Define Variables

Create a variables.tf file and add the following:

variable "filename" {
  default = "/home/ubuntu/terraform-tutorials/terraform-variables/demo-var.txt"
}

variable "content" {
  default = "This is coming from a variable which was updated"
}

Here:

  • filename specifies the file path where the file will be created.

  • content defines the content of the file.

Step 2: Use Variables in main.tf

Create a main.tf file and add:

resource "local_file" "devops" {
  filename = var.filename
  content  = var.content
}

This resource creates a local file using the variables defined earlier.

Step 3: Execute Terraform Commands

Run the following commands to deploy the configuration:

terraform init
terraform plan
terraform apply

After execution:

  • Verify the file at /home/ubuntu/terraform-tutorials/terraform-variables/demo-var.txt.

  • The file should contain:
    This is coming from a variable which was updated

Task 2: Demonstrate Usage of List, Set, and Object Data Types

Data Types Overview

  1. List: An ordered collection of values. Example: ["item1", "item2"]

  2. Set: A collection of unique values. Example: ["item1", "item2"]

  3. Object: A complex data structure with attributes and values. Example:

     { key1 = "value1", key2 = "value2" }

Step 1: Define Variables

In variables.tf, add:

variable "my_list" {
  type = list(string)
  default = ["apple", "banana", "cherry"]
}

variable "my_set" {
  type = set(string)
  default = ["terraform", "devops", "automation"]
}

variable "my_object" {
  type = object({
    name = string
    age  = number
  })
  default = {
    name = "John Doe"
    age  = 30
  }
}

Step 2: Use Variables in main.tf

Modify main.tf to demonstrate the usage of these data types:

output "list_example" {
  value = var.my_list
}

output "set_example" {
  value = var.my_set
}

output "object_example" {
  value = var.my_object
}

Step 3: Apply Configuration

Run the following commands to see outputs:

terraform plan
terraform apply

Check the output:

list_example = [
  "apple",
  "banana",
  "cherry"
]
set_example = [
  "terraform",
  "devops",
  "automation"
]
object_example = {
  "name" = "John Doe"
  "age" = 30
}

Step 4: Use terraform refresh

The terraform refresh command updates the state file with the latest configuration and data.

Run:

terraform refresh

This ensures your state file reflects the latest changes from the configuration.

Key Takeaways

  1. Why Use Terraform Variables?

    • Simplify management of dynamic inputs.

    • Reuse configurations across environments.

    • Maintain modular and scalable infrastructure.

  2. Data Types in Terraform

    • List: Store ordered collections.

    • Set: Store unique, unordered collections.

    • Object: Structure complex configurations with named attributes.

  3. Best Practices

    • Use variables.tf for centralizing variables.

    • Use terraform refresh to synchronize state files.

    • Leverage terraform apply and terraform plan to preview and apply changes.

Screenshots for Validation

Make sure to take screenshots:

  1. Before applying configurations: Output of terraform plan.

  2. After applying configurations: Terminal output and file contents.

  3. State refresh: Output of terraform refresh.

Conclusion

Terraform variables unlock the potential for modular, flexible infrastructure code. By practicing the tasks above, you’ll gain hands-on experience in variable management and learn how to implement advanced data structures like Lists, Sets, and Objects. Keep experimenting and refining your Terraform skills!

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