Terraform Basics - Variables and Outputs

This section is based on the configuration created in the previous section.

Variables

Define a variable in a file like this.

variables.tf


variable "container_name" {
  description = "name of the container"
  type        = string
  default     = "Container1"
}

Update a resource to use a variable:

main.tf


resource "docker_container" "nginx" {
  image = docker_image.nginx.image_id
  name  = var.container_name
  ports {
    internal = 80
    external = 8080
  }
}

Apply the updated configuration like this:

terraform apply

You can override a variable during apply like this:

terraform apply -var "container_name=container2"

Outputs

You can define outputs that will be exposed when creating infrastructure.

outputs.tf


output "container_id" {
   description = "ID of the Docker container"
   value       = docker_container.nginx.id
}

output "image_id" {
  description = "ID of the Docker image"
  value       = docker_image.nginx.id
}

You can also query the outputs with the following command after infrastructure has been built.

terraform output