How to use Terraform variables in different ways

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Introduction to Terraform variables

Just like in other technologies, variables let you customize your Terraform modules and resources without altering the modules’ code. Results you do not need to hard code just for a few tweaks in your resources.

Using variables is very handy when you are creating the same resources but with different configurations.

For example:

S3 bucket for diffrent regions
EC2 instances of diffrent sizes
Different type of ami of EC2 instances
And so on & much more…

Different ways to use Terraform variables

1. Interactive Input – terraform variables

Just don’t give default value. Terraform will ask for value at the runtime of the creation of resources.
[Note: Best Practice is to keep all variables in separate vars.tf file in the same directory]

vars.tf

variable "con" {
  description = "Enter content of demo.txt file"
  type = string
}

main.tf

resource "local_file" "demo" {
  content = var.con
  filename  = "demo.txt"
}

When you perform terraform apply terraform will ask you for a value of your variable.

2. Command-line variables

You can pass command line variables at the time of apply action

Syntax: $ terraform apply -var “<varname>=<value>”

main.tf

variable "con" {
  description = "Enter content of demo.txt file"
  type = string
}
resource "local_file" "demo" {
  content = var.con
  filename  = "demo.txt"
}

Run the apply command

terrform apply -var "con=hello terraform"

3. Variable file .tfvars

main.tf

variable "con" {
  description = "Enter content of demo.txt file"
  type = string
  default = "default value of this variable"
}
resource "local_file" "demo" {
  content = var.con
  filename  = "demo.txt"
}

terraform.tfvars