Terraform

Basics

Command	Description
terraform init	initialize a new Terraform configuration
terraform plan	preview changes to infrastructure before applying
terraform apply	apply changes to infrastructure
terraform destroy	destroy the infrastructure created by Terraform
terraform state	view and manage the Terraform state file
terraform output	view the output values of Terraform resources
terraform import	import existing infrastructure into Terraform

Configuration

Command	Description
provider	define the provider (e.g. AWS, Google Cloud) for the Terraform configuration
resource	define a resource to be managed by Terraform (e.g. EC2 instance, Cloud SQL database)
data	define data sources (e.g. AMIs, VPCs) that can be used in the Terraform configuration
module	define a reusable Terraform module to be used in the configuration
variable	define variables to be used in the Terraform configuration
output	define output values to be shown after running Terraform

State

Command	Description
terraform state list	list all resources in the Terraform state file
terraform state show	show details about a resource in the Terraform state file
terraform state mv	move a resource in the Terraform state file
terraform state rm	remove a resource from the Terraform state file

Modules

Command	Description
terraform get	download any modules required for the configuration
terraform init -upgrade	upgrade any modules to the latest version
terraform module list	list all modules used in the Terraform configuration

Workspaces

Command	Description
terraform workspace new	create a new workspace
terraform workspace select	switch to a different workspace
terraform workspace list	list all workspaces

Syntax

The most commonly used Terraform blocks are:

• Provider Block: Specifies the cloud provider and its configuration.
• Resource Block: Defines the infrastructure resources to be managed, such as instances, networks, or databases.
• Variable Block: Declares input variables that can be customized when running Terraform.
• Output Block: Displays the values of certain resources after Terraform applies the configuration.
• Data Block: Retrieves and uses information from external data sources.
• Module Block: Calls reusable modules that encapsulate a set of resources and configurations.

Provider block

provider "aws" {
  region = "us-west-2"
}

Resource block

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
}

Variable block

variable "region" {
  type    = string
  default = "us-west-2"
}

Output block

output "instance_ip" {
  value       = aws_instance.example.private_ip
  description = "Private IP address of the instance"
}

Data block

data "aws_subnet" "example" {
  id = "subnet-12345678"
}

Module block

module "vpc" {
  source  = "./modules/vpc"
  vpc_cidr_block = var.vpc_cidr_block
  subnets        = var.subnets
}

Directory Structure

├── main.tf
├── variables.tf
├── outputs.tf
├── terraform.tfvars
├── modules/
│   └── <module_name>/
│       ├── main.tf
│       ├── variables.tf
│       └── outputs.tf
├── environments/
│   ├── dev/
│   │   ├── main.tf
│   │   ├── variables.tf
│   │   └── outputs.tf
│   ├── prod/
│   │   ├── main.tf
│   │   ├── variables.tf
│   │   └── outputs.tf
│   └── staging/
│       ├── main.tf
│       ├── variables.tf
│       └── outputs.tf
├── .terraform/
└── terraform.tfstate

• main.tf: Contains the main Terraform configuration for your project, including resource blocks and provider configuration.
• variables.tf: Defines input variables used in the main configuration, allowing customization and flexibility.
• outputs.tf: Declares output values that you want to display or use in other parts of your infrastructure.
• terraform.tfvars: Contains variable values specific to your project. (It's recommended to keep this file out of version control and use different tfvars files for each environment.)
• modules/: Directory containing reusable modules, each with its own set of .tf files for configuration.
• environments/: Directory for organizing environment-specific configurations. Each subdirectory represents a different environment (e.g., dev, prod, staging).
• .terraform/: Directory where Terraform stores its local state and provider plugins.
• terraform.tfstate: File that captures the state of your infrastructure. (It's recommended to use remote state storage for team collaboration and state management.)

Naming Convention

• Use descriptive names: Choose names that accurately describe the purpose or function of each resource, module, or variable.
• Be consistent: Maintain a consistent naming convention throughout your project to ensure clarity and readability.
• Avoid special characters: Stick to alphanumeric characters and underscores, as some cloud providers may have restrictions on naming.