Terraform Registry Guide: How to Use Terraform Modules?

Infrastructure as Code allows controlling IT resources through code and offers reliable, reproducible, and flexible environments. Terraform is a popular IaC tool due to its scalability, strong community support, and efficient use of modules. These modules make infrastructure management easier by promoting reusability, scalability, and efficiency. The Terraform Registry further simplifies IaC by providing access to a wide range of community-contributed and official modules.

In this article, we will examine in detail how to successfully utilize Terraform modules from the Terraform Registry. This will allow you to get a better understanding in relation to these technologies and speed up your tasks.

#What are Terraform modules?

A Terraform module is a set of standard configuration files stored in its own dedicated folder. A module can contain resources, user-defined parameters, and return values. It can additionally have other modules, which assist in organizing and clarifying infrastructure code. By using modules, developers can standardize configurations, promote reuse, and improve the maintainability of their codebases.

#Types of Terraform modules

In Terraform, modules are the building blocks for organizing and managing complex infrastructure. The Terraform Registry includes two primary categories of modules: official modules and community-contributed modules. Based on how they’re shared, modules can also be classified as either local or published. At the core of this structure are two key types: root modules and child modules, which define how configurations are structured and reused.

#Root module

The root module is essentially any Terraform setup you build. Therefore, every Terraform setup you create, regardless of its simplicity, is considered a root module. Even if it’s merely a single main.tf file containing a local variable, it still qualifies as a root module. It might sound tricky, but think of it this way. Any Terraform setup can be reused as a module in other setups.

#Child module

A child module in Terraform is any module called from within the root module. Child modules are independent units with their own configurations and functions. This modular approach allows you to break down complex infrastructure into smaller, reusable components, promoting code reuse and keeping the project organized and manageable. For example, you might create a child module for a database and call it multiple times with different configurations.

module  "database" {  
    source = "./modules/database"  
}

You can call the same module multiple times and configure it differently each time.

#Local module

A local module is simply a module that hasn’t been published anywhere. You call it by specifying the location to where it’s saved locally on your system.

#Published module

A published module, on the other hand, is one that can be discovered in the Terraform Registry or tracked in a version control system via a tag. To utilize it, you reference its URL, whether it’s from the registry or your version control system.

#What is the Terraform registry?

As I’ve mentioned before, the Terraform Registry is the official channel for distributing and sharing Terraform modules. It functions as a platform where users may search for, utilize, and contribute to modules for a wide variety of cloud providers and services. There are two fundamental sorts of modules found in the Terraform registry, official modules and community modules.

• Official modules: These are hosted and managed by HashiCorp and represent core recommended practices of using Terraform. They go through thorough testing and have new updates launched frequently.

• Community modules: Community-contributed modules are broad and versatile. They are not as well supported as official modules but can be useful.

#Searching for modules in the Terraform registry

Searching for modules in the Terraform Registry is a simple task, thanks to its intuitive search functionality. Developers can enter keywords to find appropriate modules. Additionally, the Registry provides filters and categories to refine search results, allowing users to quickly locate the modules they need.

#Filters and categories

The available filters in the Terraform Registry include the following.

• Provider: Specify the cloud provider, such as AWS, Azure, or GCP.

• Module type: Filter by official or community modules.

• Tags: Use tags to find modules related to specific functionalities, such as networking or storage.

To illustrate, a person who wants to deploy AWS infrastructure may search for modules related to Amazon VPC or EC2 instances. Searching for the lines of "AWS VPC", the user would have no trouble locating various modules that assist in VPC configuration complete with documentation on how to use them.

#Using Terraform modules from the registry

After an appropriate module has been found in the Terraform Registry, the next move is to add it to your Terraform setup. Follow the steps given below to integrate it effectively.

1. Locate the module: Start by finding the module in the Registry and copying its source URL.

2. Add to configuration: In your Terraform setup document, you can specify the module with the syntax given below.

module  "example" {  
    source = "terraform-aws-modules/vpc/aws"  
    version = "v2.0.0"  
...  
}

3. Establish input parameters: Depending on the module, you’ll be required to establish the essential input parameters, such as CIDR blocks, instance types, etc.

4. Output variables: Optionally, you can specify output variables that the module will return, allowing you to reference them elsewhere in your configuration.

#Key components

When using a module from the Registry, it’s essential to understand a few key components.

• Source: The module's source URL in the Registry.

• Version: Indicate the version to prevent breaking changes during updates.

• Input/Output variables: Variables that modify the module's behavior and return values for additional use.

Here’s an illustration of a fundamental setup for establishing an AWS VPC through a module.

provider "aws" {  
    region = "us-west-2"  
}  
  
module "vpc" {  
    source = "terraform-aws-modules/vpc/aws"  
    version = "v2.0.0"  
      
    name = "my-vpc"  
    cidr = "10.0.0.0/16"  
      
    azs = ["us-west-2a", "us-west-2b"]  
    private_subnets = ["10.0.1.0/24", "10.0.2.0/24"]  
    public_subnets = ["10.0.3.0/24", "10.0.4.0/24"]  
      
    tags = {  
        Name = "my-vpc"  
    }  
}

In this example, the module creates a VPC with specified CIDR blocks, availability zones, and subnets.

#Customizing Terraform modules

While modules provide a foundation for infrastructure deployment, customizing them for specific needs is often necessary. Here are the steps to appropriately customize a Terraform module.

Download the module: The first step is to download or checkout the module directly from the Terraform Registry or the Git repository. This does not limit you to only viewing the module but helps you modify it as per the requirements as you have access to the source code and configuration files.

Modify input variables: Each module is designed to accept certain input variables that help in its functioning. Open the variables.tf file in the module directory to review the existing input variables. You can customize these variables in your Terraform configuration file by defining values that align with your infrastructure requirements. For example, if the module includes an input variable for the region, you might specify the AWS region where you want to deploy resources.

Adjust output variables: Output variables are used to capture information from the module after deployment. Review the outputs.tf file in the module directory to identify the existing output variables. You can modify these variables to capture specific data that is important for your use case, such as the bucket name or ARN of the deployed resources.

Assume you need to customize an AWS S3 module to set some bucket policies. You could create a local copy of the module and modify the main.tf file to include custom policies.

resource "aws_s3_bucket"  "my_bucket" {  
    bucket = var.bucket_name  
    acl = "private"  
      
    lifecycle {  
        prevent_destroy = true  
    }  
}  
  
resource "aws_s3_bucket_policy"  "my_bucket_policy" {  
    bucket = aws_s3_bucket.my_bucket.id  
      
    policy = <<EOF  
{  
    "Version": "2012-10-17",  
    "Statement": [  
        {  
        "Effect": "Allow",  
        "Principal": "*",  
        "Action": "s3:GetObject",  
        "Resource": "${aws_s3_bucket.my_bucket.arn}/*"  
        }  
    ]  
}  
EOF  
}

In this example, the bucket policy allows public read access to objects in the S3 bucket.

#Best practices for using Terraform modules

The use of best practices while implementing Terraform modules improves the reliability and upkeep of infrastructure and related services.

#Versioning modules

Versioning modules is crucial for guaranteeing consistency across deployments. By pinning module versions, you can avoid unexpected changes that may arise from updates.

#Avoiding module overuse

While modules promote reusability, overusing them can lead to unnecessary complexity. It’s essential to assess whether a module truly adds value to your infrastructure or if creating a custom solution would be more effective.

#When to create custom modules

It could be worthwhile to consider developing a specialized module if you find yourself having to customize a module repeatedly due to it not meeting your requirements. This approach reduces the risk of version conflicts and enhances clarity.

#Contributing to the Terraform registry

The Terraform Registry is an open platform. Therefore, users are encouraged to contribute their own modules. The steps for creating and publishing a module to the Terraform Registry are as follows.

1. Develop the Module: Create your module, ensuring it adheres to naming conventions and follows best practices.

2. Document the Module: Write clear documentation that outlines how to use the module, including input and output variables, examples, and any dependencies.

3. Publish the Module: Submit your module to the Registry, following the submission guidelines provided by HashiCorp.

#Naming and documenting Terraform modules

When naming your Terraform module take note to give names that are self-explanatory in the sense that they denote the real function of the module. With the right naming convention, the module's overall usefulness will increase and the Terraform Registry will become more standardized. In addition to naming, thorough documentation is very important. Your documentation should provide understandable examples and detailed usage instructions to guide users in implementing the module effectively.

#Common issues and troubleshooting

Despite the robustness of Terraform and its modules, users may encounter common issues.

#Typical errors

Below are two common issues to be aware of.

• Version mismatch: Using incompatible versions of modules can lead to deployment failures. Always check module compatibility before upgrading.

• Variable conflicts: Make sure that variable names are distinct to prevent conflicts between modules.

#Debugging tips

Here are some key Terraform CLI commands and techniques for debugging issues with modules.

• terraform plan: Shows what changes will be made to your infrastructure and helps identify issues.

• terraform apply: Attempt to apply the configuration and see any errors that arise during deployment.

• terraform console: Opens an interactive console that allows you to inspect variables and module outputs.

• terraform state list/show: Lists and shows resource details from Terraform's state to troubleshoot specific resources.

• terraform refresh: Syncs Terraform’s state with actual infrastructure. Deprecated as of Terraform 1.5. Refreshing is now integrated into the terraform plan and terraform apply commands automatically.

• terraform validate: Checks for syntax errors and config issues before applying changes.

• Logs and debugging: Use the TF_LOG environment variable to set the log level for Terraform operations. For example, setting export TF_LOG=DEBUG can provide in-depth information on what's happening during execution.

By using these commands and techniques, you can effectively troubleshoot common issues when using Terraform modules.

Also read: How to use Ansible with Terraform

#Conclusion

Throughout this article, you’ve learned how to search for and use modules from the Terraform Registry, customize them for specific needs, and follow best practices like versioning. With the knowledge gained from Terraform modules, users can automate complex infrastructure setups, reducing manual work and errors.

Moreover, you can contribute your custom modules to the Terraform Registry while promoting collaboration and sharing with the broader community. We encourage you to experiment with various Terraform modules to optimize your IaC implementations. Your infrastructure objectives can be effectively met by using Terraform modules. These modules will simplify the process, whether you're dealing with a complex architecture or deploying a basic resource.