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Day 7 – Type Constraints in Terraform

#30daysofawsterraform #devops #aws #terraform

On day 5 we have seen the variables in action. Today we will be doing a deep dive into type constraints in Terraform. A Terraform variable has certain types: primitive, complex, and special. We will start with primitive first.

1. Primitive Types

The word itself explains this type. Primitive means the basic ones, which include string, number, and bool.

String

It can have any text value.
Example:

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

Numeric values integers as well as floats.
Example:

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

Boolean value (true/false).
Example:

variable "is_enabled" {
  type = bool
  default = true
}
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2. Complex Types

Complex types are types that allow you to group multiple values.

List

Its an ordered collection of values of the same type.

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

Its a collection of unique values, also of the same type, but order does not matter.

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

Its an ordered collection of values of different types.

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

Its a set of string keys with values of the same type.

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

Its a collection of attributes with different types, similar to a struct.

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

Any

Allows any data type Terraform will accept whatever is provided.
Useful for flexible modules. We should avoid using it.

variable "input" {
  type = any
}
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Null

It represents the absence of a value and is often used to trigger default behavior.

Example:

variable "instance_type" {
  default = null
}
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Terraform will use the default from the provider/resource when null is passed.

Type Constraints in Terraform

How These Types Help in Real Terraform Projects

Strings for Naming Resources 

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

resource "aws_s3_bucket" "example" {
  bucket = "${var.environment}-app-data"
}
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Change environment once → everything updates.

Numbers for Scaling Resources 

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

resource "aws_instance" "server" {
  count = var.instance_count
  ami   = "ami-123"
  instance_type = "t2.micro"
}
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Increase the number → Terraform creates more servers.

Booleans for Feature Toggles 

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

resource "aws_instance" "server" {
  monitoring = var.monitoring_enabled
}
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Turn monitoring on/off with a single variable.

Lists for Repeating Resources 

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"
}
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Subnets automatically created across multiple AZs.

Maps for Centralized Tagging 

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

resource "aws_vpc" "main" {
  tags = var.tags
}
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Manage all tags from one place.

Objects for Clean, Structured Config 

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
}
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for more information checkout
https://github.com/ankitgadling/terraformwithaws/tree/main/day_7

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