Variables manipulation in Terraform

Configuring Terraform: Variables Manipulation

In this tutorial, we will cover how to configure and manipulate variables in Terraform. Variables in Terraform allow you to parameterize your configuration, making it more flexible and reusable.

Defining Variables

Variables are defined using the variable block. You can specify the type, default value, and description of the variable. Create a file named variables.tf and define some variables:

variable "region" {
  description = "The AWS region to deploy resources in"
  type        = string
  default     = "us-west-2"
}

variable "instance_type" {
  description = "The type of EC2 instance"
  type        = string
  default     = "t2.micro"
}

variable "instance_count" {
  description = "The number of EC2 instances to deploy"
  type        = number
  default     = 1
}

Using Variables in Configuration

To use the defined variables in your configuration, reference them with the var keyword. Update your main.tf file to use these variables:

provider "aws" {
  region = var.region
}

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = var.instance_type
  count         = var.instance_count
}

Setting Variable Values

You can set variable values in several ways:

1. Command-Line Flags

Set variable values directly from the command line using the -var flag:

terraform apply -var="region=us-east-1" -var="instance_type=t3.micro"

2. Terraform.tfvars File

Create a file named terraform.tfvars and define the variable values:

region = "us-east-1"
instance_type = "t3.micro"
instance_count = 2

Terraform automatically loads variables from this file if it's present in the working directory.

3. Environment Variables

Set environment variables using the TF_VAR_ prefix:

export TF_VAR_region="us-east-1"
export TF_VAR_instance_type="t3.micro"
export TF_VAR_instance_count=2

4. Variable Files

Specify variable files using the -var-file flag. Create a file named custom.tfvars:

region = "us-east-1"
instance_type = "t3.micro"
instance_count = 2

Apply the configuration using the variable file:

terraform apply -var-file="custom.tfvars"

Validating and Applying Configuration

To validate your configuration, use the terraform validate command:

terraform validate

If there are no errors, you can apply the configuration:

terraform apply

Conclusion

By defining and manipulating variables in Terraform, you can create more flexible and reusable configurations. This tutorial covered how to define variables, reference them in your configuration, and set their values using different methods.