Terraform Tutorial — Variable Types

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Terraform variables support a rich type system. Understanding types ensures your configuration catches errors early and communicates clearly what inputs it expects.

Primitive Types

Type Example HCL Literal
string AWS region "us-east-1"
number Instance count 3
bool Feature flag true 
variable "region" {
  type    = string
  default = "us-east-1"
}

variable "instance_count" {
  type    = number
  default = 2
}

variable "enable_monitoring" {
  type    = bool
  default = true
}

Collection Types

list(type)

An ordered collection:

variable "availability_zones" {
  type    = list(string)
  default = ["us-east-1a", "us-east-1b"]
}

variable "ports" {
  type    = list(number)
  default = [80, 443, 8080]
}

map(type)

Key-value pairs:

variable "tags" {
  type = map(string)
  default = {
    Environment = "dev"
    Team        = "backend"
  }
}

variable "instance_types" {
  type = map(string)
  default = {
    dev  = "t3.micro"
    prod = "t3.large"
  }
}

set(type)

Like a list but with no duplicates and no order:

variable "allowed_cidrs" {
  type    = set(string)
  default = ["10.0.0.0/8", "172.16.0.0/12"]
}

Structural Types

object({})

A map with a defined schema:

variable "database" {
  type = object({
    engine         = string
    version        = string
    instance_class = string
    storage_gb     = number
    multi_az       = bool
  })

  default = {
    engine         = "postgres"
    version        = "15.4"
    instance_class = "db.t3.micro"
    storage_gb     = 20
    multi_az       = false
  }
}

tuple([])

A list with a defined sequence of types:

variable "cidr_config" {
  type    = tuple([string, number])
  default = ["10.0.0.0", 16]
}

List of Objects

The most common complex type in real projects:

variable "users" {
  type = list(object({
    name  = string
    email = string
    admin = bool
  }))

  default = [
    { name = "alice", email = "alice@example.com", admin = true },
    { name = "bob",   email = "bob@example.com",   admin = false },
  ]
}

The any Type

Use any when the type isn’t known in advance:

variable "settings" {
  type    = any
  default = {}
}

⚠️ Warning: Avoid any when possible. Explicit types catch errors early and serve as documentation.

What’s Next?

You know the types. Now let’s learn how to declare variables properly with descriptions, defaults, and validation.

← Variables Hub Declaring Variables →

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