Input Variables

Input variables are like arguments for a module. They are declared using the keyword variable. By defining input variables, you can flexibly modify the configuration without altering the source code of the module. You can use default values, CLI options, or environment variables to set the input variables' values.

variable "iamge_id" {
  type        = string
  description = "image id of Ubuntu 1804"
}

variable "availability_zone_name" {
  type    = string
  default = 
}

source    version    providers    count    for_each    lifecycle    depends_on    locals

A variable block contains the following arguments:

• type: specifies the type of a variable. The default value is string.
• description: describes the usage of a variable.
• default: specifies the default value of a variable. A variable with a default value can be regarded as an optional variable.
• validation block: specifies the customized validation rules of a variable.

If no variable type is specified, the default value string is used. You are advised to explicitly specify variable types; they can serve as helpful reminders for users of the module, and they allow Terraform to return a helpful error message if the wrong type is used. Terraform input variables support the following types:

• Basic types: string, number, and bool
• Compound types: list(<TYPE>), set(<TYPE>), map(<TYPE>)

The following example defines a variable of the compound type:

variable "availability_zone_names" {
  type    = list(string)
  default = []
}

variable "docker_ports" {
  type = list(object({
    internal = number
    external = number
    protocol = string
  }))
  default = [{
    internal = 8300
    external = 8300
    protocol = "tcp"
  }]
}

variable "iam_user_password" {
    type        = string
    description = "The password for iam user to log in."

    validation {
      condition     = length(var.iam_user_password)>=8
      error_message = "The password is too short."
    }
}

The condition argument is a Boolean expression. You can use a can function to check whether an error will be caused by the expression. Example:

variable "iam_user_name" {
    type        = string
    description = "This name is used for iam user to log in."

    validation {
      # regex(...) If the variable fails to match the following condition, an error is returned.
      condition     = can(regex("([a-zA-Z])", var.iam_user_name))
      error_message = "Incorrect user name. Please check whether it contains upper and lower case letters."
    }
}

If the result of condition is false, Terraform generates an error message that contains the character string defined by error_message. The value of error_message must include at least a complete sentence that starts with an uppercase letter and ends with a period (.) or question mark (?).

# variables.tf
variable "vpc_cidr" {
  type        = string
  description = "the CIDR of VPC"
}

# main.tf

• With the -var command line option.
• In variable definitions (.tfvars) files, either specified on the command line or automatically loaded.
• As environment variables.

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

A variable definitions (.tfvars) file uses the same basic syntax as the configuration files, but consists only of variable name assignments:

vpc_name = "my_vpc"
vpc_cidr = "192.168.0.0/16"
availability_zone_names = [
]

Terraform also automatically loads variable definitions files if they are present:

• Files named exactly terraform.tfvars or terraform.tfvars.json
• Any files with names ending in .auto.tfvars or .auto.tfvars.json

Files whose names end with .json are parsed instead as JSON objects.

{
    "vpc_name": "my_vpc"
}

Note that the same variable cannot be assigned multiple values within a single source.

For more information about variables, see Input Variables in the Terraform documentation.