Module 2, HCL Syntax From Scratch

What is HCL

HCL stands for HashiCorp Configuration Language. It is designed to be human-readable and machine-friendly.

The Four Building Blocks

1, Blocks

Everything in Terraform is a block. A block has a type, optional labels, and a body:

block_type "label_one" "label_two" {
  argument = value
}

Real example:

resource "aws_s3_bucket" "my_bucket" {
  bucket = "my-company-data"
}

• resource, block type
• "aws_s3_bucket", resource type (label 1)
• "my_bucket", local name (label 2)
• bucket = "my-company-data", argument

2, Arguments

name               = "finpay"           # string
port               = 3000               # number
enabled            = true               # boolean
availability_zones = ["us-east-1a", "us-east-1b"]  # list
tags = {
  Environment = "production"
  Team        = "platform"
}

3, Expressions

# Reference another resource
subnet_id = aws_subnet.public.id

# String interpolation
name = "finpay-${var.environment}"

# Conditional (ternary)
instance_type = var.environment == "production" ? "t3.small" : "t3.micro"

# Function call
bucket_name = lower("MyBucket")

4, Comments

# Single line comment

/*
  Multi-line comment
  Useful for explaining complex resources
*/

Data Types

region    = "us-east-1"           # string
port      = 5432                  # number
multi_az  = false                 # bool
subnets   = ["subnet-abc", "subnet-def"]  # list(string)
tags      = { Name = "finpay-db" }        # map(string)

# object
database = {
  engine  = "postgres"
  version = "15"
  port    = 5432
}

Lab 1, Your First HCL File

mkdir terraform-lab-01
cd terraform-lab-01
touch main.tf

Write this in main.tf:

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
}

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

resource "aws_s3_bucket" "first_bucket" {
  bucket = "my-terraform-learning-bucket-12345"

  tags = {
    Name        = "My First Terraform Bucket"
    Environment = "learning"
  }
}

Then run:

terraform init    # downloads the AWS provider
terraform plan    # shows what will happen
terraform apply   # creates the bucket
terraform destroy # deletes the bucket

warning

Observe each output carefully. terraform plan is the most important command you will ever run.

Knowledge Check

1. What are the four main components of an HCL block?
2. What is the difference between a string and a number in HCL?
3. Write an HCL expression that creates a name using string interpolation with a variable called app_name.
4. What is the difference between a list and a map?
5. Why does terraform init need to run before terraform plan?

Exam Mapping

• HashiCorp Associate Obj 3: Understand Terraform basics
• HashiCorp Associate Obj 6: Navigate Terraform workflow