Terraform Common Variable Attributes

In Terraform, when defining variables, several attributes can be specified to control their behavior. Here are the primary attributes you can use when defining variables in Terraform:

1. type: Specifies the type of the variable.

   Valid types are :

   string, number, bool, list(type), set(type), map(type), object({key=type,...}), and tuple([type,...]).

    variable "instance_count" {
      type = number
    }
   

2. description: Provides a description of the variable. This is useful for documentation purposes.

    variable "instance_type" {
      description = "The type of EC2 instance to create"
      type        = string
    }
   

3. default: Sets a default value for the variable. If no value is provided by the user, this default value will be used.

    variable "instance_type" {
      type    = string
      default = "t2.micro"
    }
   

4. validation: Provides custom validation rules for the variable. You can use this to enforce constraints on the variable's value.

    variable "instance_type" {
      type = string
      validation {
        condition     = contains(["t2.micro", "t2.small", "t2.medium"], var.instance_type)
        error_message = "The instance type must be one of t2.micro, t2.small, or t2.medium."
      }
    }
   

5. sensitive: If set to true, prevents the variable's value from being displayed in Terraform's output.

    variable "db_password" {
      type      = string
      sensitive = true
    }
   

6. nullable: If set to false, the variable must be provided a non-null value. The default is true, allowing null values.

    variable "domain_name" {
      type     = string
      nullable = false
    }
   

Example

Here is an example that incorporates multiple attributes:

variable "instance_type" {
  description = "The type of EC2 instance to create"
  type        = string
  default     = "t2.micro"
  validation {
    condition     = contains(["t2.micro", "t2.small", "t2.medium"], var.instance_type)
    error_message = "The instance type must be one of t2.micro, t2.small, or t2.medium."
  }
}

variable "db_password" {
  description = "The password for the database"
  type        = string
  sensitive   = true
  nullable    = false
}

These attributes allow you to define variables in a way that includes type safety, default values, validations, and sensitive data handling, making your Terraform configurations more robust and easier to manage.