Terraform - Modules

Modules in Terraform are self-contained packages of Terraform configurations that are managed as a group. Modules are used to create reusable components in Terraform as well as for basic code organization.

Can find Terraform Module here: Terraform Module Registry

Module basics

Any set of Terraform configuration files in a folder is a module. E.g.,

1. Create folder layout

   ├─module
   │  └─s3
   │          main.tf
   │          outputs.tf
   │          variables.tf
   │          user-data.sh
   │
   └─qa
       └─service
             main.tf
             outputs.tf
             variables.tf

2. Create a module to set S3

   # S3
   resource "aws_s3_bucket" "terraform_module" {
   	bucket = "yongfeiuall-terraform-module"
   	versioning {
   		enabled = true
   	}
   }

3. Using a module

   provider "aws" {
   	region = "ap-northeast-1"
   }
   
   module "module-test" {
   	source = "../../module/s3"
   }

4. Run terraform init, terraform plan and terraform apply commands

   D:\terraform\ModuleStudy\qa\service>terraform init
   Initializing modules...
   - module.module-test  Getting source "../../module/s3"

Module inputs

Modules can have input parameters, too. To define them, you use a
mechanism you’re already familiar with: input variables.

1. Open ‘\module\s3\variables.tf’, and add

   variable "yongfeiuall_module_bucket" {
   description = "The name of the S3 bucket"
   }

2. Open ‘\module\s3\main.tf’, and update

   # S3
   resource "aws_s3_bucket" "terraform_module" {
   	bucket = "{var.yongfeiuall_module_bucket}"
   	versioning {
   		enabled = true
   	}
   
   }

3. Open ‘\qa\servicemodule\s3\main.tf’, and update

   provider "aws" {
   	region = "ap-northeast-1"
   }
   
   module "module-test" {
   	source = "../../module/s3"
   	
   	yongfeiuall_module_bucket = "yongfeiuall_variable"
   }

4. Run terraform init, terraform plan and terraform apply commands

Module outputs

Outputs are a way to tell Terraform what data is important.

1. Open ‘\module\s3\output.tf’, and add

   output "s3_bucket_name" {
   value = "${aws_s3_bucket.terraform_module.bucket}"
   }

2. Open ‘\qa\servicemodule\s3\main.tf’, and update: add a security group, which name is use s3 bucket name.

   provider "aws" {
   	region = "ap-northeast-1"
   }
   
   module "module-test" {
   	source = "../../module/s3"
   	
   	yongfeiuall_module_bucket = "yongfeiuall_variable"
   }
   
   resource "aws_security_group" "http" {
   	name = "${module.module-test.s3_bucket_name}"
   
   	# HTTP access from anywhere
   	ingress {
   		from_port   = "${var.server_port}"
   		to_port     = "${var.server_port}"
   		protocol    = "tcp"
   		cidr_blocks = ["0.0.0.0/0"]
   	}
   	  
   	# Outbound internet access
   	egress {
   		from_port   = 0
   		to_port     = 0
   		protocol    = "-1"
   		cidr_blocks = ["0.0.0.0/0"]
   	}
   	lifecycle {
   		create_before_destroy = true
   	}
   }

3. Run terraform init, terraform plan and terraform apply commands
   

Module versioning

We recommend explicitly constraining the acceptable version numbers for each external module to avoid unexpected or unwanted changes.

Module Repo

instead of using a folder you can use a git repository to version your module.

• Parameters
  The URLs for Git repositories support the following query parameters:

  # ref - The ref to checkout. This can be a branch, tag, commit, etc.
  
  module "consul" {
    source = "git::https://hashicorp.com/consul.git?ref=0.0.2"

Terraform Registry

You can use a specific version for a module if you are using a module registry like the Terraform Registry。

module "consul" {
  source = "git::https://hashicorp.com/consul.git"

  version = "0.0.2

The Terraform Registry is a public registry. For private use you must use the Private Registry available ine the Enterprise version.

Terrafile

Manages external Terraform modules, controlled by a Terrafile.
Refer here Terrafile for detail infomation.

Module gotchas

File paths

By default, Terraform interprets the path relative to the current working directory. That works if you’re using the file function in a Terraform configuration file that’s in the same directory as where you’re running terraform apply.

You can use path.module to convert to a path that is relative to the module folder.

data "template_file" "user_data" {
	template = "${file("${path.module}/user-data.sh")}"
	
	vars {
	}
}