Day 7 – Type Constraints in Terraform

Source: Dev.to

Primitive Types

Primitive types are the basic building blocks: string, number, and bool.

variable "name" {
  type    = string
  default = "Terraform"
}

variable "age" {
  type    = number
  default = 25
}

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

Complex Types

Complex types let you group multiple values.

List (ordered collection of same‑type values)

variable "instance_ids" {
  type = list(string)
}

Set (unique values, order not significant)

variable "unique_tags" {
  type = set(string)
}

Tuple (ordered collection of different types)

variable "my_tuple" {
  type = tuple([string, number, bool])
}

Map (string keys with same‑type values)

variable "region_mapping" {
  type = map(string)
}

Object (attributes with different types, similar to a struct)

variable "server_config" {
  type = object({
    name = string
    cpu  = number
    prod = bool
  })
}

Special Types

any (accepts any Terraform data type)

variable "input" {
  type = any
}

null (represents the absence of a value, often used to trigger default behavior)

variable "instance_type" {
  default = null
}

Practical Examples

Environment‑based naming

variable "environment" {
  type    = string
  default = "dev"
}

resource "aws_s3_bucket" "example" {
  bucket = "${var.environment}-app-data"
}

Changing environment updates all dependent resources.

Scalable instance count

variable "instance_count" {
  type    = number
  default = 3
}

resource "aws_instance" "server" {
  count         = var.instance_count
  ami           = "ami-123"
  instance_type = "t2.micro"
}

Increasing instance_count creates additional servers.

Toggle monitoring

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

resource "aws_instance" "server" {
  monitoring = var.monitoring_enabled
}

Turn monitoring on/off with a single variable.

Multi‑AZ subnets

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

resource "aws_subnet" "subnet" {
  count      = length(var.availability_zones)
  az         = var.availability_zones[count.index]
  cidr_block = "10.0.${count.index}.0/24"
}

Subnets are automatically created across the specified AZs.

Centralized tagging

variable "tags" {
  type = map(string)
  default = {
    Environment = "dev"
    Owner       = "teamA"
  }
}

resource "aws_vpc" "main" {
  tags = var.tags
}

Manage all tags from a single place.

Composite configuration object

variable "config" {
  type = object({
    region         = string
    monitoring     = bool
    instance_count = number
  })

  default = {
    region         = "us-east-1"
    monitoring     = true
    instance_count = 2
  }
}

provider "aws" {
  region = var.config.region
}

Further Reading

For more information, see the repository:

https://github.com/ankitgadling/terraformwithaws/tree/main/day_7