Configurations

Updated Jun 11, 2022 ·

Root Module

This is a directory on the local filesystem containing all the configuration files and code files. This is typically consists of three files:

main.tf
variables.tf
outputs.tf
provider.tf

This root directory may also contain:

terraform.state
terraform.state.backup

Core Files

`main.tf`

This file contains the core configurations:

Resources
Provider
Data Sources

This file can be modularized by splitting the sections into their own separate .tf files.

provider "aws" {
  region = "ap-southeast-1"
}

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = var.instance_type
}

`variables.tf`

This file contains all possible variables referenced in the main.tf file.

variable "region" {
  description = "AWS region to deploy resources"
  type        = string
  default     = "ap-southeast-1"
}

variable "instance_type" {
  description = "Type of EC2 instance"
  type        = string
  default     = "t2.micro"
}

`outputs.tf`

This is used to explicitly export values after you ran terraform apply.

Outputs can be references within any parent templates
Often used to create modules

Example:

output "instance_public_ip" {
  description = "The public IP of the EC2 instance"
  value       = aws_instance.example.public_ip
}

output "instance_id" {
  description = "The ID of the EC2 instance"
  value       = aws_instance.example.id
}

`terraform.tfvars` vs `variables.tf`

Based on a Stack Overflow discussion:

The difference between these files is declaration vs. assignment.

variables.tf is where variables are declared.
terraform.tfvars is where variable values are assigned.

Example declaration:

variable "example" {}

This tells Terraform that the module accepts an input variable called example. You can then reference it anywhere using var.example.

There are several ways to assign values to variables:

Use -var on the terraform plan or terraform apply command
Use -var-file to load a .tfvars file with multiple variable values
Create a terraform.tfvars or .auto.tfvars file, which Terraform loads automatically
Assign values directly when calling a child module

You can also set default values in the variable declaration to make them optional:

variable "example" {
  default = "default_value"
}

Note that new variables cannot be created in terraform.tfvars. All variables must first be declared in variables.tf.

In smaller setups, you can declare and assign values in the same file for simplicity.

References

Resources

A Terraform Resource describes an infrastructure object. It tells Terraform what to create, how it should be configured, and which provider should manage it.

Defines an infrastructure object like a VM, database, or network
Includes all configuration details such as CPU, memory, disk, and interfaces
Terraform sends this definition to the provider to create the actual resource

Here is a simple AWS EC2 instance resource. It tells Terraform to create a small EC2 instance using the specified AMI.

resource "aws_instance" "web" {
  ami           = "ami-a1b2c3d4"
  instance_type = "t2.micro"
}

The resource documentation shows all supported resources for a provider.

Root Module​

Core Files​

main.tf​

variables.tf​

outputs.tf ​

terraform.tfvars vs variables.tf​

Resources​