2 — Variables¶

Folder: 01-basics/2-variable-use/

variable blocks are inputs — like function arguments. Declared in variables.tf with a type and a default, referenced as var.name.

The code¶

main.tf creates two resources, only one of which writes a file:

resource "local_file" "fruits" {
  filename = var.fileName
  content  = var.content
}

resource "random_pet" "my_pet" {
  prefix    = var.prefix
  separator = var.separator
  length    = var.name_length
}

variables.tf declares five inputs, each with a type and a default:

variable "fileName" {
  description = "The path where the file will be created"
  type        = string
  default     = "/tmp/helloFruits.txt"
}

variable "content" {
  description = "The content to write into the file"
  type        = string
  default     = "Hello World! Default Text coming from the variable"
}

variable "prefix" {
  description = "The prefix for the random pet name"
  type        = string
  default     = "Mrs"
}

variable "separator" {
  description = "The separator for the random pet name"
  type        = string
  default     = "-"
}

variable "name_length" {
  description = "The length of the random pet name"
  type        = number
  default     = 1
}

Run it¶

terraform init && terraform apply
cat /tmp/helloFruits.txt

# override without touching the code — CLI beats default
terraform apply -var='content=overridden from the command line'

A resource that produces no file¶

random_pet.my_pet writes nothing to disk. It exists only in state:

terraform state show random_pet.my_pet

That's the only way to see it. A resource doesn't have to produce an artifact you can cat — it just has to be something the provider can create, track and destroy.

Precedence — the gotcha that costs real time¶

Create a terraform.tfvars setting content, then also edit the default in variables.tf to something different. Which one wins?

echo 'content = "from tfvars"' > terraform.tfvars
terraform apply
cat /tmp/helloFruits.txt

The tfvars value wins, and the default is never used. Full order, lowest to highest:

default  <  terraform.tfvars  <  *.auto.tfvars  <  -var-file  <  -var  <  TF_VAR_*

This exact rule cost real debugging time in Session 2, and it bites again in Stage 3 where the project ID is set in two places at once. The GCP version of this experiment is Lab 15.

An unused declared variable is a smell¶

Worth checking as a habit: every variable declared in variables.tf should actually be referenced somewhere. A declared-but-unused variable is either a leftover from a refactor or a wiring bug where the code hardcodes what it should read from var. Terraform will not warn you about either.

Key takeaway¶

A default is the value of last resort, not the value — every other source outranks it. So when a config behaves as though your edit didn't happen, don't edit harder: work out which layer is actually supplying the value first. That one habit is most of what this page is for.

Theory: §7 Variables & locals · Quiz: Variables, expressions & guards · Next: Locals