Why resources are Terraform's core - Why It Works

Introduction

Terraform manages infrastructure by defining resources that represent real-world components like servers or databases. Resources are the main building blocks that Terraform creates, updates, and deletes to match your desired setup.

When you want to create a virtual machine in the cloud to run your application

When you need to set up a database instance for storing your app data

When you want to configure a network with subnets and firewalls for security

When you need to manage cloud storage buckets for your files

When you want to automate the setup of any cloud service or infrastructure component

Config File - main.tf

main.tf

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

resource "aws_instance" "example" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"

  tags = {
    Name = "example-instance"
  }
}

The provider block tells Terraform which cloud to use and where.

The resource block defines a virtual machine (EC2 instance) with a specific image and size.

Terraform uses this resource to create and manage the server in the cloud.

Commands

This command sets up Terraform in your folder by downloading the necessary plugins for AWS. It prepares Terraform to work with your configuration.

Terminal

terraform init

Expected Output

Initializing the backend...



Initializing provider plugins...

- Finding latest version of hashicorp/aws...

- Installing hashicorp/aws v4.0.0...

- Installed hashicorp/aws v4.0.0 (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.

This command shows what Terraform will do to reach the desired state. It previews creating the EC2 instance without making any changes yet.

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:



  # aws_instance.example will be created

  + resource "aws_instance" "example" {

      + ami           = "ami-0c55b159cbfafe1f0"

      + instance_type = "t2.micro"

      + tags          = {

          + "Name" = "example-instance"

        }

    }



Plan: 1 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 changes to create the EC2 instance. The flag skips the confirmation prompt to speed up the process.

Terminal

terraform apply -auto-approve

Expected Output

aws_instance.example: Creating...

aws_instance.example: Still creating... [10s elapsed]

aws_instance.example: Creation complete after 20s [id=i-0abcd1234efgh5678]



Apply complete! Resources: 1 added, 0 changed, 0 destroyed.

→

-auto-approve - Skips manual approval to apply changes immediately

This command displays the current state of the infrastructure Terraform manages, showing details of the created EC2 instance.

Terminal

terraform show

Expected Output

aws_instance.example:

  id = i-0abcd1234efgh5678

  ami = ami-0c55b159cbfafe1f0

  instance_type = t2.micro

  tags = {

    Name = example-instance

  }

Key Concept

If you remember nothing else from this pattern, remember: resources are the real things Terraform creates and manages to build your infrastructure.

Common Mistakes

Writing a resource block with missing required fields like AMI or instance type

Terraform cannot create the resource without essential information, causing errors during apply

Always include all required fields for each resource type as documented

Running terraform apply before terraform init

Terraform needs to download provider plugins first; skipping init causes errors

Always run terraform init first to prepare the working directory

Not running terraform plan before apply

You miss the chance to review changes, which can lead to unexpected infrastructure updates

Run terraform plan to preview changes before applying

Summary

Define resources in Terraform files to represent real infrastructure components.

Use terraform init to prepare Terraform and download providers.

Use terraform plan to preview changes and terraform apply to create or update resources.