> For the complete documentation index, see [llms.txt](https://devops-3.gitbook.io/devops/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://devops-3.gitbook.io/devops/docs/module-12-iac/modules.md).
# Modules
The capability to generate reusable infrastructure components known as modules is one of the primary characteristics that contribute to Terraform power.
A Terraform module is a collection of standard configuration files in a dedicated directory. Terraform modules encapsulate groups of resources dedicated to one task, reducing the amount of code you have to develop for similar infrastructure components.
Modules
### Benefits of Modules
* Reusability
* Code Reduction
* Organization
* Consistency
* Parameterization
* Management
Resources Vs Modules
A resource in Terraform describes a piece of infrastructure that is going to be created (e.g., a VPC, a subnet, an ec2 instance, etc).
A module is a collection of resources that are used together to achieve a reusable use case.
Terraform Modules Workflow
Workflow
A typical module would resemble this:
```hcl
.
ec2_instance
├── main.tf
├── variables.tf
└── outputs.tf
```
### Types of Modules
1. Root Module
2. Child Module
3. Local Module
4. Published Module
Module Types
### Define Module
Within your primary Terraform setup, you can call and instantiate modules using the modules block.
```hcl
module "module_name" {
source = "path_of_module"
[other_arguments]
}
```
Example
```hcl
provider "aws" {
region = "us-east-2"
}
module "test_server" {
source = "./ec2_instance"
instance_type = "t2.micro"
ami_id = "ami-98656754364"
}
output "instance_id" {
value = module.test_server.instance_id
}
```
1. Root Module
The root module consists of all the resources defined in the .tf files in a Terraform configuration, meaning that all Terraform configurations have their own root module.
Even if you are simply creating a main.tf that has just a locals block inside of it with a local variable, that is still considered a root module.
2. Child Module
Every module can call other modules, and all of the modules called inside another module are considered child modules.
Calling a child module means to include all the resources defined in that module in the current configuration. This is done by using a module block inside your Terraform configuration:
```hcl
module "webservers" {
source = "../webserver"
}
```
3. Local Module
A local module is a module that wasn’t published in any registry and when it is sourced, it is using the path to that particular module.
4. Published Module
A published module refers to a module that has been pushed to a Terraform Registry, or even simply on a VCS and has a tag associated with it. When a published module is sourced, the URL of that module is used either from the registry or from the VCS itself
