Understand Infrastructure as Code (IaC) Concepts

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Overview

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HCL (HashiCorp Configuration Language) is a declarative language used by Terraform to define infrastructure resources.

HCL Resource Block

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resource "local_file" "pet" {
    filename = "/root/pets.txt"
    content  = "We love pets!"
}

This file would be called local.tf.

Key Terminology

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Note: A resource is an object that Terraform manages.

Provisioning a Resource

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There are four steps to provision a resource:

1. Write the configuration file.
2. Initialize the directory.
3. Plan the deployment.
4. Apply the configuration.

Terraform Commands

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Updating and Destroying Infrastructure

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resource "local_file" "pet" {
    filename = "/root/pets.txt"
    content  = "We love pets and animals!"
    file_permission = "0644"
}

Running terraform plan shows 1 to add — this is because we added a new argument called file_permission. When we run terraform apply, it will update the existing resource with the new argument.

Note: terraform apply will destroy and recreate the resource because we changed an argument that cannot be updated in place.

terraform destroy will destroy the resource defined in the configuration file. It will prompt you to confirm the destruction before proceeding. Once confirmed, Terraform will remove the resource from your infrastructure.

Multiple Resources

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Terraform will create everything under the root folder. For example, given two separate resource files:

resource "local_file" "pet" {
    filename = "/root/pets.txt"
    content  = "We love pets!"
}

resource "local_file" "pet2" {
    filename = "/root/pets2.txt"
    content  = "We love pets and animals!"
}

When we run terraform apply, it will create both pets.txt and pets2.txt under the root folder.

You can also put both resources in a single file:

resource "local_file" "pet" {
    filename = "/root/pets.txt"
    content  = "We love pets!"
}

resource "local_file" "pet2" {
    filename = "/root/pets2.txt"
    content  = "We love pets and animals!"
}

This file, called main.tf, will create both pets.txt and pets2.txt under the root folder when we run terraform apply.

Common Terraform File Conventions

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Related notes

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Part of my Terraform Associate certification series:

1. Understand Infrastructure as Code (IaC) Concepts (this note)
2. Terraform Provider Basics
3. Variables, Resource Attributes, and Dependencies
4. Terraform State
5. Using the Terraform CLI