> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Parameterizing Configurations with Input Variables

> Explains using Terraform input variables to parameterize modules for reusable, environment aware, and maintainable infrastructure

Welcome — this lesson explains Terraform `variable` blocks and how to use input variables to make your infrastructure code flexible, reusable, and environment-aware. You'll learn why hard-coded values are problematic, how variables solve those problems, and the anatomy of a `variable` block so you can parameterize your Terraform modules effectively.

## The problem with hard-coded values

Managing multiple environments (production, QA, development) often leads to nearly identical resource blocks that differ only by values. Hard-coding those values causes duplication, increases maintenance effort, and makes configuration drift likely.

Example of duplicated, hard-coded resources:

```hcl theme={null}
resource "azurerm_resource_group" "prd" {
  name     = "example-resources"
  location = "West Europe"
}

resource "azurerm_virtual_network" "vnet" {
  name                = "example-network"
  resource_group_name = "example-resources"
  location            = "West Europe"
  address_space       = ["10.0.0.0/16"]
}

resource "azurerm_mssql_database" "db1" {
  name      = "example-db"
  server_id = "server_db"
  collation = "sql_general"
}

resource "azurerm_resource_group" "dev" {
  name     = "example-resources"
  location = "West Europe"
}

resource "azurerm_virtual_network" "dev" {
  name                = "example-network"
  resource_group_name = "example-resources"
  location            = "West Europe"
  address_space       = ["10.0.0.0/16"]
}

resource "azurerm_mssql_database" "db2" {
  name      = "example-db"
  server_id = "server_db"
  collation = "sql_general"
}

resource "azurerm_resource_group" "test" {
  name     = "example-resources"
  location = "West Europe"
}

resource "azurerm_virtual_network" "test" {
  name                = "example-network"
  resource_group_name = "example-resources"
  location            = "West Europe"
  address_space       = ["10.0.0.0/16"]
}

resource "azurerm_mssql_database" "db3" {
  name      = "example-db"
  server_id = "server_db"
  collation = "sql_general"
}
```

Repeating the same resource definitions violates DRY (Don't Repeat Yourself). Changes like updating `location` or `address_space` require many edits, increasing the chance of errors and drift.

## How variables solve the problem

Parameterize configuration values into `variable` blocks and centralize environment-specific values in `.tfvars` files or CI/CD pipeline inputs. A single Terraform module becomes the shared, validated source of truth; teams and environments only supply different values.

<Frame>
  <img src="https://mintcdn.com/kodekloud-c4ac6d9a/HUZ-SFw2Tg4GUikN/images/HashiCorp-Certified-Terraform-Associate-004/Terraform-Configuration-Fundamentals/Parameterizing-Configurations-with-Input-Variables/terraform-variables-presentation-slide.jpg?fit=max&auto=format&n=HUZ-SFw2Tg4GUikN&q=85&s=1b46385ecfd5b2c00741db7621f7ca50" alt="The image is a presentation slide discussing using variables in Terraform, showing teams (Cloud Ops, QA, Dev) on the left and different environments (Production, QA, Development) on the right with characteristics of the Development Environment." width="1920" height="1080" data-path="images/HashiCorp-Certified-Terraform-Associate-004/Terraform-Configuration-Fundamentals/Parameterizing-Configurations-with-Input-Variables/terraform-variables-presentation-slide.jpg" />
</Frame>

Benefits:

* Consistency: All environments use the same, tested configuration.
* Collaboration: Teams provide variable files (e.g., `prod.tfvars`, `dev.tfvars`) without touching shared modules.
* Maintainability: One change in the core module propagates across environments.
* Scalability: To add an environment, create one variable file—no template copying.

Example converted to use variables:

```hcl theme={null}
resource "azurerm_resource_group" "prd" {
  name     = var.rg_name
  location = var.rg_location
}

resource "azurerm_virtual_network" "dv" {
  name                = var.net_name
  resource_group_name = var.net_rg
  location            = var.net_location
  address_space       = var.net_cidr
}

resource "azurerm_mssql_database" "dbl" {
  name      = var.mssql_name
  server_id = var.server_id
  collation = var.collation
}
```

Ways to supply values for `var.*`:

* `terraform.tfvars` or `*.tfvars` files (e.g., `prod.tfvars`, `dev.tfvars`)
* Environment-specific `.tfvars` files referenced by `-var-file`
* `-var` CLI flags (for ad-hoc overrides)
* CI/CD variable injections or remote state-based workflows

This pattern enables “one configuration, many deployments.”

## What is a variable block?

A `variable` block declares an input to the module or root module. It defines a named parameter and optional metadata:

* `description`: human-readable text
* `type`: input type (validates input values)
* `default`: fallback value when no value is provided

If you omit `type`, Terraform will attempt to infer it from a default or provided value, but explicit types catch errors earlier.

<Frame>
  <img src="https://mintcdn.com/kodekloud-c4ac6d9a/HUZ-SFw2Tg4GUikN/images/HashiCorp-Certified-Terraform-Associate-004/Terraform-Configuration-Fundamentals/Parameterizing-Configurations-with-Input-Variables/purple-puzzle-pieces-variable-block-terraforms.jpg?fit=max&auto=format&n=HUZ-SFw2Tg4GUikN&q=85&s=2d84018c9cdd8101ec061aa543e93221" alt="The image features a set of purple puzzle pieces on the left and a description on the right about &#x22;Variable Block&#x22; in HashiCorp Terraform, emphasizing the use of variable blocks for customizable and reusable configurations." width="1920" height="1080" data-path="images/HashiCorp-Certified-Terraform-Associate-004/Terraform-Configuration-Fundamentals/Parameterizing-Configurations-with-Input-Variables/purple-puzzle-pieces-variable-block-terraforms.jpg" />
</Frame>

Basic example:

```hcl theme={null}
variable "vsphere_datacenter" {
  description = "Name of datacenter"
  type        = string
  default     = "prd-workload-dc"
}
```

List example:

```hcl theme={null}
variable "vsphere_networks" {
  description = "List of networks"
  type        = list(string)
  default     = [
    "VM Network",
    "Management Network"
  ]
}
```

<Callout icon="lightbulb" color="#1CB2FE">
  If you omit `type`, Terraform will try to infer it from a default or from input values; explicit types, however, help catch configuration errors early.
</Callout>

### Anatomy of a variable block

| Element     | Purpose                                 | Example                                                      |
| ----------- | --------------------------------------- | ------------------------------------------------------------ |
| Name        | Identifier used as `var.<name>` in code | `variable "rg_name" {}`                                      |
| Description | Documents intent for maintainers        | `description = "Resource group name"`                        |
| Type        | Validates shape and primitive types     | `type = string`, `type = list(string)`, `type = map(number)` |
| Default     | Fallback value if nothing is provided   | `default = "dev-resources"`                                  |

Common Terraform types: `string`, `number`, `bool`, `list(<type>)`, `map(<type>)`, `object({...})`, and `any`.

### Example: variable definitions and use

variables.tf

```hcl theme={null}
variable "rg_name" {
  description = "Resource group name"
  type        = string
  default     = "example-resources"
}

variable "net_cidr" {
  description = "VNet address space"
  type        = list(string)
  default     = ["10.0.0.0/16"]
}
```

prod.tfvars

```hcl theme={null}
rg_name  = "prod-resources"
net_cidr = ["10.1.0.0/16"]
```

Apply:

```bash theme={null}
terraform init
terraform plan -var-file="prod.tfvars"
terraform apply -var-file="prod.tfvars"
```

<Callout icon="warning" color="#FF6B6B">
  Avoid committing sensitive values into `.tfvars` in version control. Use Terraform Cloud/Enterprise, Vault, environment variables, or CI/CD secret stores to manage secrets securely.
</Callout>

## Quick reference — how to provide variable values

| Method                               | Precedence | Typical use                         |
| ------------------------------------ | ---------- | ----------------------------------- |
| `-var` CLI flag                      | Highest    | Temporary overrides                 |
| `-var-file`                          | High       | Environment-specific files in CI/CD |
| Environment variable `TF_VAR_<name>` | Medium     | CI agents or scripts                |
| `terraform.tfvars` / `*.tfvars`      | Lower      | Local defaults for developers       |
| `default` in `variable` block        | Lowest     | Module fallback                     |

## Summary

Input variables let you parameterize Terraform modules so a single, shared configuration can be safely reused across environments. Define the contract in `variable` blocks (name, description, type, default) and supply environment-specific values via `.tfvars`, CLI flags, or pipeline variables. This reduces duplication, improves maintainability, and minimizes configuration drift.

Next steps:

* Explore variable types in detail (`object`, `map`, `tuple`)
* Learn patterns for structuring `.tfvars` per environment
* Investigate best practices for handling sensitive data with Vault or Terraform Cloud

## Links and references

* [Terraform Input Variables](https://www.terraform.io/language/values/variables)
* [Terraform CLI: Specifying Variables](https://www.terraform.io/cli/commands#input-variables)
* [HashiCorp Best Practices for Variables](https://www.hashicorp.com/resources)

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