Terraform

Terraform is an infrastructure-as-code (IaC) software tool created by HashiCorp.

Index

• Install
• Usage
• Files
• Backends
• Modules

Install

HashiCorp distributes Terraform as a binary package.

• Go to the Downloads page.
• Download the precompiled binary.
• Add the precompiled binary to the PATH.

Usage

Check version.

terraform version

Initialize a working directory.

terraform init

Reconfigure a backend.

terraform init -reconfigure

Migrate the state to a backend.

terraform init -migrate-state

Download and update modules mentioned in the root module.

terraform get

Rewrite configuration files to a canonical format and style.

terraform fmt
terraform fmt -recursive

Validate the configuration files without accessing any remote service.

terraform validate

Create an execution plan to preview changes in the infrastructure.

terraform plan

Execute the actions proposed in a plan.

terraform apply

Destroy all remote resources of a plan.

terraform destroy

Files

File	Tracked In	Purpose
*.tf	✅ Git	Infrastructure code
.terraform.lock.hcl	✅ Git	Locks provider versions
terraform.tfstate	✅ Backend	Infrastructure state
.terraform/	❌ Local	Caches provider plugins and modules

Backends

A backend is a mechanism that determines how and where store state, and how to handle state locking and remote operations.

1. Create AWS S3 bucket for storage.

• Block all public access.
• Enable versioning.
• Enable server side encryption.

2. Create AWS DynamoDB table for locking mechanism.

• Partition key: LockID.

3. Use backend.

terraform {
  backend "s3" {
    bucket         = "terraform-state-bucket"
    key            = "terraform.tfstate"
    region         = "eu-west-1"
    dynamodb_table = "terraform_state_table"
  }
}

4. Migrate the state to the backend.

terraform init -migrate-state

5. Delete local state files.

Modules

A module is a container for multiple resources that are used together.

Configuration with multiple providers and modules.

root
├── main.tf
├── modules.tf
├── submodule1
│   ├── main.tf
│   ├── modules.tf
│   ├── submodule2
|   |   ├── main.tf
|   |   └── ...
│   ├── submodule3
|   |   ├── main.tf
|   |   └── ...
│   └── ...
└── ...

At root module, main.tf file.

terraform {
  required_providers {
    aws = {
      source = "hashicorp/aws"
    } 
  }
}

provider "aws" {
  alias = "prov1"
  # ...
}

provider "aws" {
  alias = "prov2"
  # ...
}

At root module, modules.tf file.

module "submodule1" {
  source = "./submodule1"
  providers = {
    aws.prov1 = aws.prov1
    aws.prov2 = aws.prov2
  }
} 

At submodule1 module, main.tf file.

terraform {
  required_providers {
    aws = {
      source = "hashicorp/aws"
      configuration_aliases = [
        aws.prov1,
        aws.prov2,
      ]
    } 
  }
}

At submodule1 module, modules.tf file.

module "submodule2" {
  source = "./submodule2"
  providers = {
    aws = aws.prov1
  }
} 

module "submodule3" {
  source = "./submodule3"
  providers = {
    aws = aws.prov2
  }
}

At submodule2 and submodule3 modules, main.tf file.

terraform {
  required_providers {
    aws = {
      source = "hashicorp/aws"
    } 
  }
}