Terraform is a popular tool for managing infrastructure as code (IaC). It allows you to define your infrastructure in a declarative manner, and to manage it using the same tools and processes that you use for your application code. One of the key features of Terraform is the ability to use modules to organize and reuse your infrastructure code.

What are Terraform modules?

Terraform modules are a way to organize and reuse your infrastructure code. They allow you to create a collection of Terraform resources, and to package them into a self-contained unit that can be easily shared and used by other Terraform configurations. This makes it easier to manage your infrastructure, and to reduce duplication and complexity in your Terraform code.

How to create and use Terraform modules

To create a Terraform module, you need to create a directory and put your Terraform configuration files in it. You can then use the module keyword in your Terraform configuration to reference the module, and to specify any input variables values that the module needs. Here is an example of a Terraform module that creates an Amazon VPC:

# vpc/variables.tf
variable "cidr_block" {
  type        = string
  description = "The CIDR block for the VPC."
}

# vpc/main.tf
resource "aws_vpc" "vpc" {
  cidr_block = var.cidr_block
}

# vpc/outputs.tf
output "vpc_id" {
  value = aws_vpc.vpc.id
}

To use the module, you can include it in your Terraform configuration by specifying the path to the module’s directory, and by providing any input variables that the module requires:

# main.tf

module "vpc" {
  source = "./vpc"

  vpc_cidr_block = "10.0.0.0/16"
}

The resources defined in a module are encapsulated, so you cannot access their attributes directly. You can however reference the outputs produced by the module in your Terraform configuration. For example, you can use the vpc_id output defined in the module to create subnets in your VPC:

# main.tf

resource "aws_subnet" "subnet" {
  vpc_id     = module.vpc.vpc_id
  cidr_block = "10.0.1.0/24"
}

Using remote Terraform modules

You can include modules from other git repositories or even from the Terraform Registry.

To use a module from a git repository, you can specify the URL of the repository in the source attribute of the module block. You can also specify a specific branch or tag to use:

module "vpc" {
  source = "git@github.com:my-org/tf-vpc.git?ref=v3.0.0"

  # [input variables]
}

Best practices for using Terraform modules

Here are some best practices for using Terraform modules:

Keep your modules small and focused: A Terraform module should be small and focused, and should only contain the resources that are needed to accomplish a specific task. This will make your modules easier to understand and maintain, and will make it easier to reuse them in different contexts.
Use input and output variables: Use input and output variables to make your modules more flexible and reusable. Input variables allow you to specify the configuration of your module when you use it, and output variables allow you to access the values produced by your module in other parts of your Terraform configuration.
Use version control for your modules: Use version control for your modules to keep track of changes to your module’s configuration. This will allow you to revert to previous versions of your module if necessary, and to collaborate with other team members on your modules.

By following these best practices, you can use Terraform modules effectively to manage your infrastructure as code. This will help you to organize and reuse your infrastructure code, and to maintain the reliability and stability of your infrastructure.

Conclusion

In this blog post, we have discussed what Terraform modules are, how to create and use them, and some best practices for using Terraform modules. By using Terraform modules, you can organize and reuse your infrastructure code, and to manage your infrastructure more efficiently and effectively. This will help you to reduce duplication and complexity in your Terraform code, and to maintain the reliability and stability of your infrastructure.