Terraform - Input Variables

  1. Installing Terraform
  2. What is Terraform and Why do we need it?
  3. Terraform Commands
  4. Hashicorp Configuration Language - HCL
  5. Tainting and Untainting Resources
  6. Terraform Console and Output
Input variables serve as parameters for a Terraform file. A variable block configures a single input variable for a Terraform module. Each block declares a single variable.

Syntax:

variable [NAME] {
  [OPTION] = "[VALUE]"
}
Arguments
Within the block body (between { }) is configuration for the variable, which accepts the following arguments:

type (Optional): If set, this defines the type of the variable. Valid values are string, list, and map.
default (Optional): This sets a default value for the variable. If no default is provided, Terraform will raise an error if a value is not provided by the caller.
description (Optional): A human-friendly description for the variable.
Using variables during an apply:
terraform apply -var 'foo=bar'
Set up the environment:

cd terraform/basics
Edit main.tf:

vi main.tf
main.tf contents:

#Define variables
variable "image_name" {
  description = "Image for container."
  default     = "ghost:latest"
}
variable "container_name" {
  description = "Name of the container."
  default     = "blog"
}
variable "int_port" {
  description = "Internal port for container."
  default     = "2368"
}
variable "ext_port" {
  description = "External port for container."
  default     = "80"
}
# Download the latest Ghost Image
resource "docker_image" "image_id" {
  name = "${var.image_name}"
}
# Start the Container
resource "docker_container" "container_id" {
  name  = "${var.container_name}"
  image = "${docker_image.image_id.latest}"
  ports {
    internal = "${var.int_port}"
    external = "${var.ext_port}"
  }
}
#Output the IP Address of the Container
output "IP Address" {
  value       = "${docker_container.container_id.ip_address}"
  description = "The IP for the container."
}
output "container_name" {
  value       = "${docker_container.container_id.name}"
  description = "The name of the container."
}

Validate the changes:

terraform validate
Plan the changes:

terraform plan
Apply the changes using a variable:

terraform apply -var 'ext_port=8080'
Change the container name:

terraform apply -var 'container_name=ghost_blog' -var 'ext_port=8080'
Reset the environment:

terraform destroy -var 'ext_port=8080'

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