Introduction

In this lesson we cover Terraform variables: how to declare them, how they make configurations reusable and environment-agnostic, and the common patterns for supplying values. Variables let you parameterize your Terraform configuration instead of hard-coding values. This makes code easier to reuse across environments (dev, staging, prod), simplifies CI/CD automation, and reduces duplication. Agenda for this lesson:

Define input variables in Terraform
- Externalize values such as region, resource names, SKUs, subscriptions, and environment-specific settings.
Understand the variable block
- Learn the structure and purpose of the variable block, including metadata such as type, default, and description. Note that the variable’s name is declared in the block header (e.g., variable "name" { ... }) rather than as a field inside the block.
Supply values to variables
- Explore ways to provide variable values: .tfvars files, command-line arguments (-var and -var-file), environment variables, and interactive prompts.
Work with Terraform variable types
- Review primitive types (string, number, bool) and complex types (list, map, object) with usage examples.

The image presents an agenda with four points about using input variables in Terraform configurations, including defining variables, understanding variable blocks, setting variable values, and identifying data types. The agenda is visually organized with numbered markers and a gradient background.

Use variables to decouple environment-specific data from configuration. This enables the same Terraform codebase to provision different environments by supplying different variable values.

We will now start by looking at how to declare input variables and the structure of a variable block.

Declaring input variables

A variable block defines an input variable for a module or root module. The block header contains the variable name; attributes inside define metadata and constraints. Basic example:

variable "location" {
  description = "Azure region where resources will be deployed"
  type        = string
  default     = "eastus"
}

Key attributes:

description — human-readable context for the variable
type — the data type (e.g., string, number, bool, list(string), map(string), object({...}))
default — optional value used if none is supplied
sensitive — optional boolean to mark values as sensitive (prevents them from being shown in CLI output)

Example showing a mix of types, including map and object:

variable "tags" {
  description = "Tags applied to resources"
  type        = map(string)
  default = {
    environment = "dev"
    owner       = "team-a"
  }
}

variable "vm_sizes" {
  description = "Allowed VM SKUs for this environment"
  type        = list(string)
  default     = ["Standard_B1s", "Standard_B2s"]
}

variable "service_config" {
  description = "Configuration object for the service"
  type = object({
    sku               = string
    capacity          = number
    enable_monitoring = bool
  })
  default = {
    sku               = "standard"
    capacity          = 2
    enable_monitoring = true
  }
}

Referencing variables inside your configuration uses the var namespace:

resource "azurerm_resource_group" "rg" {
  name     = "rg-${var.service_config.sku}"
  location = var.location
  tags     = var.tags
}

Variable types — quick reference

Type	Description	Example
`string`	Simple text	`variable "name" { type = string }`
`number`	Numeric values	`variable "replicas" { type = number }`
`bool`	True / false	`variable "enabled" { type = bool }`
`list(...)`	Ordered list	`list(string)` — `["a", "b"]`
`map(...)`	Key/value collection	`map(string)` — `{ env = "dev" }`
`object({...})`	Structured object with typed attributes	`object({ sku = string, capacity = number })`

When providing examples or inline values that include braces ({}) or double-curly syntax, wrap them in backticks to avoid MDX parsing issues. For example: `[{ "object": "person", "bbox": [0,0,10,10] }]`.

Ways to supply variable values

Terraform supports multiple ways to provide values for input variables. Choose the method that fits your workflow (local testing, automation, CI/CD, or secret management).

Method	Use case	Example
`.tfvars` file	Grouped values per environment (recommended for repeated runs)	`terraform.tfvars` or `prod.tfvars`
`-var-file`	Explicitly pass a tfvars file on the CLI	`terraform apply -var-file="prod.tfvars"`
`-var`	Quick one-off values	`terraform apply -var='location=westus2'`
Environment variables	CI/CD or secrets via env vars	`export TF_VAR_location="westus2"`
Interactive prompt	When no default is provided and automation isn’t used	Terraform prompts for missing required variables

Example terraform.tfvars:

resource_name = "my-rg"
location      = "westus2"

Environment variable example:

export TF_VAR_location="westus2"
terraform apply

CLI example:

terraform apply -var='location=westus2' -var='resource_name=my-rg'

Do not commit secrets (passwords, API keys) into .tfvars files stored in version control. Use a secrets manager or mark variables sensitive = true and supply values via secure pipelines or Terraform Cloud/Enterprise variable sets.

Best practices

Prefer tfvars files for environment-level defaults and -var-file to select them at runtime.
Use typed variables (list(...), map(...), object(...)) to validate inputs and catch mistakes early.
Document variable description values to aid collaborators and automation.
Avoid hard-coding environment-specific values inside modules—pass them as inputs to keep modules reusable.

Links and references

We will next walk through concrete examples of using variables in modules and how to organize tfvars files per environment.

Infrastructure as Code Fundamentals

Terraform Cloud

Setting up environment

Azure Context for Terraform

HashiCorp Configuration Language

Terraform Providers

Variables

Outputs and Dependencies

Iteration and Logic

Advanced Constructs

Terraform State Fundamentals

Remote State

Terraform Workspaces

Terraform CLI

Lifecycle Meta-Arguments

Data Sources

Provisioners

Debugging Terraform

Terraform Modules

Azure DevOps Integration

Azure Pipelines for Terraform

Introduction

Declaring input variables

Variable types — quick reference

Ways to supply variable values

Best practices

Links and references

Watch Video

​Declaring input variables

​Variable types — quick reference

​Ways to supply variable values

​Best practices

​Links and references

Watch Video

Declaring input variables

Variable types — quick reference

Ways to supply variable values

Best practices

Links and references