Terraform Registry modules - Commands & Configuration

Introduction

Terraform Registry modules help you reuse pre-made building blocks for your cloud infrastructure. They save time by letting you add complex setups with simple code instead of writing everything from scratch.

When you want to create a virtual network with best practices without writing all the details yourself

When you need to add a managed database service quickly and correctly configured

When you want to deploy a common application setup like a web server cluster with load balancing

When you want to share your infrastructure code with others in a reusable way

When you want to keep your Terraform code clean and organized by using tested modules

Config File - main.tf

main.tf

terraform {
  required_version = ">= 1.0"
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 4.0"
    }
  }
}

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

module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "~> 3.0"

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

  azs             = ["us-east-1a", "us-east-1b", "us-east-1c"]
  public_subnets  = ["10.0.1.0/24", "10.0.2.0/24", "10.0.3.0/24"]
  private_subnets = ["10.0.101.0/24", "10.0.102.0/24", "10.0.103.0/24"]

  enable_nat_gateway = true
  single_nat_gateway = true
}

This Terraform file sets up the AWS provider and uses a module from the Terraform Registry to create a Virtual Private Cloud (VPC). The module "vpc" block pulls the VPC module from the registry, specifying the version and configuration like network ranges and availability zones. This module handles creating subnets, routing, and NAT gateways automatically.

Commands

This command downloads the module and provider plugins needed for your configuration. It prepares your working directory for Terraform commands.

Terminal

terraform init

Expected Output

Initializing the backend...



Initializing provider plugins...

- Finding hashicorp/aws versions matching "~> 4.0"...

- Installing hashicorp/aws v4.50.0...

- Installed hashicorp/aws v4.50.0 (signed by HashiCorp)



Terraform has been successfully initialized!



You may now begin working with Terraform. Try running "terraform plan" to see

any changes that are required for your infrastructure. All Terraform commands

should now work.

This command shows what Terraform will create or change based on your configuration. It helps you verify before applying.

Terminal

terraform plan

Expected Output

An execution plan has been generated and is shown below.

Resource actions are indicated with the following symbols:

  + create



Terraform will perform the following actions:



  # module.vpc.aws_vpc.main will be created

  + resource "aws_vpc" "main" {

      + cidr_block = "10.0.0.0/16"

      + enable_dns_support = true

      + enable_dns_hostnames = true

      + id = (known after apply)

      ...

    }



Plan: 10 to add, 0 to change, 0 to destroy.



─────────────────────────────────────────────────────────────────────────────



Note: You didn't specify an "-out" parameter to save this plan, so Terraform

can't guarantee to take exactly these actions if you run "terraform apply" later.

This command applies the planned changes to create the infrastructure. The flag skips manual approval to speed up the process.

Terminal

terraform apply -auto-approve

Expected Output

aws_vpc.main: Creating...

aws_vpc.main: Creation complete after 3s [id=vpc-0abcd1234efgh5678]

...

Apply complete! Resources: 10 added, 0 changed, 0 destroyed.

→

-auto-approve - Automatically approve the apply step without asking for confirmation

This command removes all the infrastructure created by Terraform. The flag skips manual approval.

Terminal

terraform destroy -auto-approve

Expected Output

aws_vpc.main: Destroying...

aws_vpc.main: Destruction complete after 2s

...

Destroy complete! Resources: 10 destroyed.

→

-auto-approve - Automatically approve the destroy step without asking for confirmation

Key Concept

If you remember nothing else from this pattern, remember: Terraform Registry modules let you reuse tested infrastructure code easily by just referencing them in your configuration.

Common Mistakes

Not running 'terraform init' before 'terraform plan' or 'apply'

Terraform won't download the module or provider plugins, causing errors.

Always run 'terraform init' first to prepare your working directory.

Using a module source without specifying a version

This can cause unexpected changes if the module updates with breaking changes.

Always specify a version constraint to keep your infrastructure stable.

Changing module source code directly inside the .terraform directory

Changes will be overwritten on the next 'terraform init' and are not tracked.

Copy the module to your own directory if you want to customize it, or use module inputs.

Summary

Use 'terraform init' to download modules and providers before planning or applying.

'terraform plan' shows what infrastructure changes will happen without applying them.

'terraform apply' creates or updates infrastructure based on your configuration and modules.

'terraform destroy' removes all created infrastructure safely.