Lab #5: Terraform Input Variables | How to Use Terraform Input Variables | Terraform Variables

Introduction

This tutorial will guide you through the use of Terraform input variables, a crucial feature for managing configurations in your infrastructure as code. Understanding how to utilize input variables effectively can enhance your Terraform scripts by making them more flexible and reusable.

Step 1: Understanding Terraform Input Variables

• Input variables allow you to customize Terraform configurations without modifying the code directly.
• They can be defined in a .tf file and are used to pass values into your Terraform modules.
• Benefits of using input variables include:
  • Improved code reusability
  • Increased flexibility in configurations
  • Easier management of different environments (e.g., development, staging, production)

Step 2: Defining a Number Input Variable

• Number input variables are used to pass numeric values. Here’s how to define one:

  variable "instance_count" {
    description = "Number of instances to create"
    type        = number
    default     = 1
  }
  

• To use this variable in your resource configuration:

  resource "aws_instance" "example" {
    count         = var.instance_count
    ami           = "ami-0c55b159cbfafe01e"
    instance_type = "t2.micro"
  }
  

• Practical Tip: Always provide a default value to avoid errors when the variable is not explicitly set.

Step 3: Using List Input Variables

• List input variables allow you to pass multiple values. Here’s how to set one up:

  variable "availability_zones" {
    description = "List of availability zones"
    type        = list(string)
    default     = ["us-east-1a", "us-east-1b"]
  }
  

• Example of using a list variable in a resource block:

  resource "aws_instance" "example" {
    count         = length(var.availability_zones)
    ami           = "ami-0c55b159cbfafe01e"
    instance_type = "t2.micro"
    availability_zone = var.availability_zones[count.index]
  }
  

• Common Pitfall: Ensure that the variable type matches the data you are passing to avoid runtime errors.

Step 4: Passing Variables at Runtime

• You can override default values at runtime using the -var flag:

  terraform apply -var="instance_count=3" -var='availability_zones=["us-east-1a", "us-east-1c"]'
  

• Alternatively, you can create a terraform.tfvars file to store your variable values:

  instance_count = 2
  availability_zones = ["us-east-1b", "us-east-1d"]
  

Conclusion

In summary, Terraform input variables are essential for creating flexible and reusable configurations. By understanding how to define and use number and list input variables, you can manage your infrastructure more effectively. As you continue to explore Terraform, consider experimenting with different variable types and configurations to enhance your deployment processes. For further learning, check out related tutorials on Terraform and infrastructure management.