Terraform Variables

Overview

• Declared in variable blocks
• Arguments:
  • default
    • Causes variable to be optional.
    • If omitted, value is set to the default argument
  • type
    • string
    • number
    • bool
    • Complex types: list(<TYPE>), set(<TYPE>), map(<TYPE>), object({<ATTR_NAME> = <TYPE>, ...}, tuple([<TYPE>, ...])
    • any
  • description
    • Variable documentation
  • validation
    • See below
  • sensitive
    • Suppresses display of value in the CLI output
    • Value still stored in plain text in state
    • Sent to provider without obfuscation
      • Could be disclosed e.g. as part of an ID
  • nullable
    • Allows/disallows null values

Validation

• In addition to type constraints.
• validation.condition must use value of variable to return true if valid, otherwise false
• Must not produce errors
  • May use can function to detect errors and return true/false
• e.g.

variable "my_id" {
  type = string
  
  validation {
    condition     = length(var.my_id) > 4 && substr(var.my_id, 0, 3) == "foo"
    error_message = "The length of my_id must be greater than 4, starting with foo"
  }
}

Setting Variables

• Precedence:
  • Environment variables—in format TF_VAR_<variable name>
  • terraform.tfvars
  • terraform.tfvars.json
  • *.auto.tfvars / *.auto.tfvars.json
  • -var / -var-file on the command line