Input Variables

About Input Variables

• Terraform offers input variables
• they are called "variables", but in fact these are parameters delivered to the current terraform module
• Variables are declared in a variable section, and they are parsed before other tf sections.
• Variables cannot reference other variables
• Variables allow default values
• They can specify a type, e.g:
  • list
  • map
  • string
• You can define values for variables using:
  • cli (when planning or applying)
  • using environment variables

Some Variable Examples

Some examples:

• A variable with a type of list(string), and a default value

1variable "availability_zone_names" {
2  type    = list(string)
3  default = ["us-west-1a"]
4}

• A complex example, of a list of docker-ports. Each port has internal and external numeric values and a protocol (whici is a string):

 1variable "docker_ports" {
 2  type = list(object({
 3    internal = number
 4    external = number
 5    protocol = string
 6  }))
 7  default = [
 8    {
 9      internal = 8300
10      external = 8300
11      protocol = "tcp"
12    }
13  ]
14}

Using Input Variable Values

• Here's how you use a variable in a resource:

1resource "aws_instance" "example" {
2  instance_type = "t2.micro"
3  ami           = var.image_id
4}

Assigning values in a .tfvars file

• To set lots of variables, it is more convenient to specify their values in a variable definitions file (with a filename ending in either .tfvars or .tfvars.json) and then specify that file on the command line with -var-file:

1terraform apply -var-file="testing.tfvars"

• A variable definitions file uses the same basic syntax as Terraform language files, but consists only of variable name assignments:

1image_id = "ami-abc123"
2availability_zone_names = [
3  "us-east-1a",
4  "us-west-1c",
5]