Terraform Module vs Resource: The Ultimate Difference

Estimated reading time: 6 minutes

Last updated on November 8th, 2024 at 02:52 pm

Introduction to Terraform

Terraform is a powerful open-source tool developed by HarshiCorp for building and managing the infrastructure safely and efficiently. Terraform enables users to define the entire infrastructure as declarative configuration languages.

With Terraform, there are two main concepts that you need to understand: “Terraform Module vs Resources”. Understanding the difference between these two is crucial for maintaining the infrastructure configuration.

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What is a Terraform Resource?

A resource is an infrastructure component that you manage, such as an EC2 instance, a S3 bucket, a database, or a DNS record.

Resource is the most basic building block of a Terraform configuration that represents the actual infrastructure service or component that Terraform will create and manage.

How to Define and Use Resources

Defining a Terraform resource is straightforward. Let’s see an example of how to create an AWS EC2 instance as a resource:

HCL
# Terraform Module vs Resource
provider "aws" {
  region = "us-west-2"
}

resource "aws_instance" "example" {
  ami           = "ami-0g45b349cbfafe1f0"
  instance_type = "t3.micro"

  tags = {
    Name = "dev-webserver-instance"
  }
}

In this example code:

  • The provider block specifies the AWS region.
  • The resource block defines an EC2 instance with an Amazon Machine Image (AMI) and instance type.
  • Tags are optional but added for identification.
Best Practices for Managing Resources
  • Meaningful names for resources make the configuration easy to understand.
  • Group the related resources logically.
  • Keep the Terraform resource blocks clear and organized.

Top 5 Terraform Module Versioning Best Practices

What is a Terraform Module?

A Module in Terraform is a group or container for multiple resources that are used together.

You can consider the modules as packages for the Terraform configurations that encapsulate multiple resources into a single reusable component that can be used across.

Once you define the Terraform module you can easily publish it and share it with teams, then they can use it with multiple Terraform projects without going deeper into the actual implementation.

Creating and Using Modules

Creating the Terraform module is simple, put and organize all the Terraform configurations into a separate directory.

HCL
# Terraform Module vs Resource
# File: main.tf
module "vpc" {
  source = "./modules/vpc"
  cidr_block = "10.0.0.0/16"
}

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

resource "aws_subnet" "subnet" {
  vpc_id     = aws_vpc.main.id
  cidr_block = "10.0.1.0/24"
}

In this example:

  • A module named “vpc” is created and called from the root configuration.
  • The module contains a VPC and a subnet resource.
  • Variables are used to pass values to the module.
Best Practices for Module Creation and Management
  • Keep the Terraform module target the specific function or service.
  • Use the input variable to make modules configurable.
  • Write the documentation for the module usage for the expected input/output.

Top 5 Terraform Module Versioning Best Practices

Terraform Module vs Resource: Module Version Best Practice

Terraform Module vs Resource: Key Differences

Scope and Reusability

  • Resources are individual components like EC2 instances or S3 buckets.
  • Modules group multiple resources into a reusable package.
  • Modules allow to reuse of common configurations across multiple projects.
  • Resources are specific to each separate configuration.

Complexity and Maintenance

  • Modules help to manage complex configurations by encapsulating the related resources.
  • Modules make it easier to understand and maintain the infrastructure.
  • The module reduces code duplication and simplifies updates.
  • Changes made within a module propagate the change to all configurations using the module.

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Terraform Modules vs Resources: Usage

CriteriaUsing ResourcesUsing Modules
SimplicitySimple configurationsComplex configurations
UniquenessUnique, non-repetitive componentsReusable across projects and environments
ScopeIndividual infrastructure elementsGroups of related resources
MaintenanceIsolated to individual resourcesCentralized updates for multiple configurations
ExamplesSingle EC2 instanceVPC with subnets, route tables, and security groups
FlexibilitySpecific to each configurationConfigurable through input variables
Version ControlVersioned with main configurationIndependently versioned modules
TestingStraightforward validationRequires additional testing for module functionality
Terraform Module vs Resource: Usage

Terraform Modules vs Resources: Best Practices

Organizing Your Terraform Code

  • Structure configuration logically and separate resources into different directories and files.
  • Use readable and descriptive files and directory names to define the purpose.

Version Control and Documentation

  • Implement the version control to track the changes and ensure consistency.
  • Write the documentation for the resource and module to provide clear usage and input/output.

Testing and Validation

  • Use terraform validate to check configuration for syntax errors.
  • Use terraform plan to view the changes before applying them.

Terraform Validate vs Plan: Understanding the Key Differences

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Terraform Module vs Resource: Comparison

CriteriaTerraform ResourceTerraform Module
DefinitionA single component that Terraform manages, such as an EC2 instance or S3 bucket.A package for multiple resources that are used together, encapsulating them for reuse.
ScopeIndividual infrastructure components.Groups of related resources, often encompassing a full application or service.
ReusabilitySpecific to each configuration; not inherently reusable.Designed for reuse across multiple configurations and projects.
Complexity ManagementSuitable for simple, straightforward configurations.VPC setup including subnets, route tables, and security groups; application deployment including backend, frontend, and database.
MaintenanceMaintenance is isolated to individual resource configurations.Centralized updates; changes to a module propagate to all configurations using it.
OrganizationDefined directly in the root configuration files.Organized in separate directories or repositories, promoting better structure.
ParameterizationLimited to the parameters defined in the resource block.Highly configurable through input variables, allowing for flexible usage.
Version ControlTypically versioned with the rest of the configuration code.Modules can be independently versioned, allowing for version control and rollback.
Examples of UseSingle EC2 instance, S3 bucket, VPC.Use meaningful names, group logically, and keep concise.
Best PracticesThe same tools apply, with additional focus on module testing independently.Keep focused, use input variables and document usage.
Testing and ValidationUse terraform validate and terraform plan for syntax and change previews.The same tools apply, with an additional focus on module testing independently.
Terraform Module vs Resource: Comparison

Conclusion

Understanding the difference between the “Terraform Module vs Resource” is essential for creating and maintaining the efficient infrastructure as code.

The resource represents individual components, whereas the module packages the group of resources for reusability.

Follow the “Terraform Module vs Resource” best practices to leverage and streamline your infrastructure.

Kashyap Merai

Kashyap Merai

Kashyap Merai, a Certified Solution Architect and Public Cloud Specialist with over 7 years in IT. He helped startups in Real Estate, Media Streaming, and On-Demand industries launch successful public cloud projects.

Passionate about Space, Science, and Computers, He also mentors aspiring cloud engineers, shaping the industry's future.

Connect with him on LinkedIn to stay updated on cloud innovations.