🌍 Terraform Public Modules: Pre-Built Community Modules

Imagine being able to deploy a production-ready VPC, Kubernetes cluster, or serverless architecture with a few lines of code — without writing every resource yourself.

That’s exactly what Terraform Public Modules enable.

Terraform’s Public Module Registry acts like an App Store for infrastructure. It’s a global repository where cloud engineers and companies publish pre-built, reusable modules that anyone can use.

These modules are open-source, community-verified, and continuously updated to follow cloud best practices.

Learning how to use and adapt public modules is a must-have skill for every DevOps, Cloud, and Data Engineer.

🔹 What Are Public Terraform Modules?

A public Terraform module is a reusable, pre-defined infrastructure package available on the Terraform Registry (https://registry.terraform.io/).

It’s created by:

• The Terraform community
• Verified providers (like AWS, Google, Azure, Kubernetes, HashiCorp)
• Organizations sharing their standardized IaC templates

Public modules save hours of development time and ensure consistency across environments.

💡 Simple Definition:

Public Modules = Pre-Built Infrastructure Blueprints Published by the community, used through Terraform Registry.

🔹 Key Features of Public Modules

🔹 Terraform Registry Overview

Explanation: Terraform users pull modules from the Registry, which hosts community, verified, and partner modules. Terraform fetches them from their GitHub sources and applies them to your cloud environment.

🔹 Why Use Public Modules?

1. Save Time — Skip writing hundreds of lines of Terraform code.
2. Leverage Best Practices — Modules are reviewed by experts and providers.
3. Avoid Errors — Pre-tested modules reduce the risk of misconfiguration.
4. Accelerate Learning — Studying community modules teaches advanced Terraform design.
5. Standardization — Teams use the same, versioned building blocks.
6. Scalability — Modules can be used in pipelines, across projects, and in automation.

🔹 How to Use Public Modules (Step-by-Step)

1. Visit Terraform Registry.

2. Search for the module you want (e.g., “AWS VPC” or “GCP Storage”).

3. Copy the usage snippet (includes source and version).

4. Paste it into your Terraform configuration.

5. Run:

   terraform init
   terraform apply

6. Terraform automatically downloads the module, resolves dependencies, and applies resources.

🔹 Module Source Formats

🔹 Example 1: AWS VPC Module (Public Registry)

🗂 Directory Structure

main.tf
outputs.tf

main.tf

provider "aws" {
  region = "us-east-1"
}

module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "5.5.1"

  name = "production-vpc"
  cidr = "10.0.0.0/16"

  azs             = ["us-east-1a", "us-east-1b"]
  private_subnets = ["10.0.1.0/24", "10.0.2.0/24"]
  public_subnets  = ["10.0.101.0/24", "10.0.102.0/24"]

  enable_nat_gateway = true
  single_nat_gateway = true

  tags = {
    Terraform   = "true"
    Environment = "production"
  }
}

outputs.tf

output "vpc_id" {
  value = module.vpc.vpc_id
}

Run:

terraform init
terraform apply

✅ Result: Creates a complete AWS VPC with private/public subnets, NAT Gateway, and routing — all with one module.

🔹 Example 2: Azure Network Module (Public Registry)

main.tf

provider "azurerm" {
  features {}
}

module "network" {
  source  = "Azure/network/azurerm"
  version = "5.2.0"

  resource_group_name = "rg-main"
  address_space       = ["10.1.0.0/16"]
  subnet_prefixes     = ["10.1.1.0/24"]
  subnet_names        = ["internal"]

  vnet_name = "core-network"
  location  = "East US"
}

outputs.tf

output "vnet_id" {
  value = module.network.vnet_id
}

✅ Result: Creates a VNet, subnets, and required configurations automatically — no manual setup.

🔹 Example 3: GCP Cloud Storage Bucket (Public Registry)

main.tf

provider "google" {
  project = "my-gcp-project"
  region  = "us-central1"
}

module "bucket" {
  source  = "terraform-google-modules/cloud-storage/google"
  version = "3.4.0"

  name     = "tf-demo-bucket"
  location = "US"
  force_destroy = true

  uniform_bucket_level_access = true
}

outputs.tf

output "bucket_name" {
  value = module.bucket.name
}

✅ Result: Creates a secure, versioned Google Cloud Storage bucket using the public module in seconds.

🔹 How to Remember the Concept (Mnemonic)

Use the word “PUBLIC”:

Memory Trick:

“Terraform PUBLIC modules are Pre-Built, Useful, Best-practice, Lightweight, Integrated, and Community-driven.”

🔹 Interview & Exam Preparation Tips

💬 Common Interview Questions:

1. Q: What is a Terraform Public Module? A: It’s a pre-built infrastructure component shared on the Terraform Registry for reuse across projects.

2. Q: How do you reference a public module from the Terraform Registry? A:

   module "example" {
     source  = "terraform-aws-modules/vpc/aws"
     version = "5.0.0"
   }

3. Q: What are “Verified” modules? A: Modules validated by HashiCorp or cloud providers, ensuring reliability and compliance.

4. Q: Why should you version-lock public modules? A: To avoid unexpected behavior due to upstream updates.

🧠 Study Technique:

Use A.C.E. method:

• A – Apply examples practically
• C – Compare different clouds’ modules
• E – Explore module source code on GitHub

Learning by doing is the best way — experiment with AWS, Azure, and GCP modules locally.

🔹 Why It’s Important to Learn This Concept

1. Accelerates Development

You can build enterprise-grade infrastructure in minutes by leveraging the community’s collective expertise.

2. Enhances DevOps Productivity

Modules allow teams to automate common architectures quickly, reducing manual coding.

3. Ensures Consistency

Public modules enforce uniform configuration patterns across environments (e.g., same tagging, network layout).

4. Improves Collaboration

Teams can contribute to or fork public modules for internal use.

5. Professional Edge

Terraform Registry usage is often a key skill in interviews and certifications, especially for roles like:

• DevOps Engineer
• Cloud Infrastructure Engineer
• Data Engineer
• Site Reliability Engineer (SRE)

6. Future-Proof Skill

As infrastructure complexity grows, modularization becomes essential. Knowing how to use public modules saves time and ensures quality.

🔹 Best Practices for Using Public Modules

🔹 Common Mistakes to Avoid

1. Not version-locking modules → May cause breaking changes after updates.

2. Using unverified modules in production → Can lead to insecure or unstable setups.

3. Ignoring input variables → Leads to misconfiguration or incorrect resource naming.

4. Overriding core logic → Avoid changing module internals unless you fork it intentionally.

🔹 Comparison: Public vs. Private Modules

🔹 Real-World Use Cases

1. Multi-Environment Deployments

   • Use same public module for dev, staging, and prod by passing different variables.

2. Cloud Foundation Setup

   • AWS: VPC, IAM Roles, S3 modules
   • Azure: VNet, Resource Groups
   • GCP: Buckets, IAM Bindings

3. CI/CD Pipelines

   • Automate module usage through Jenkins, GitHub Actions, or Terraform Cloud.

4. Hybrid Cloud Infrastructure

   • Combine public modules across multiple providers for hybrid setups.

🔹 Summary Table

🔹 Conclusion

Terraform Public Modules are the backbone of reusable cloud infrastructure. They combine community expertise, provider standards, and DevOps automation into one simple command.

Whether you’re deploying a simple S3 bucket or an enterprise-grade network, public modules let you focus on innovation, not boilerplate code.

💬 “Don’t reinvent infrastructure — reuse what the world has perfected.”

By learning to effectively discover, adapt, and version-control Terraform Registry modules, you move from writing code to designing ecosystems.

✅ Quick Recap

• Public Modules = pre-built community infrastructure components
• Available on Terraform Registry
• Examples covered: AWS VPC, Azure Network, GCP Bucket
• Mnemonic: PUBLIC
• Best practice: pin versions, use verified modules
• Essential for Terraform certification & DevOps roles