Terraform Fundamentals
Core Syntax (HCL)
\\\`hcl
terraform/main.tf
Configure the required provider
terraform {
required_version = ">= 1.6.0"
required_providers {
aws = {
source = "hashicorp/aws"
version = "~> 5.0"
}
}
# Remote state (use this in teams!)
backend "s3" {
bucket = "my-terraform-state"
key = "prod/terraform.tfstate"
region = "us-east-1"
dynamodb_table = "terraform-locks"
encrypt = true
}
}
Configure the provider
provider "aws" {
region = var.aws_region
}
Variable declaration
variable "aws_region" {
description = "AWS region to deploy into"
type = string
default = "us-east-1"
}
variable "instance_count" {
description = "Number of instances"
type = number
default = 2
}
variable "allowed_cidr" {
description = "CIDR blocks allowed to SSH"
type = list(string)
default = ["10.0.0.0/8"]
}
Local values (computed/reusable)
locals {
common_tags = {
Environment = var.environment
ManagedBy = "Terraform"
Team = "Platform"
}
}
Resource definition
resource "aws_vpc" "main" {
cidr_block = "10.0.0.0/16"
enable_dns_hostnames = true
enable_dns_support = true
tags = merge(local.common_tags, {
Name = "main-vpc"
})
}
Output values
output "vpc_id" {
description = "ID of the main VPC"
value = aws_vpc.main.id
}
\\\`
Data Sources
Data sources let you fetch existing infrastructure:
\\\`hcl
Get the latest Amazon Linux 2023 AMI
data "aws_ami" "amazon_linux" {
most_recent = true
owners = ["amazon"]
filter {
name = "name"
values = ["al2023-ami-*-x86_64"]
}
}
Reference it
resource "aws_instance" "web" {
ami = data.aws_ami.amazon_linux.id # Use the fetched AMI
instance_type = "t3.micro"
}
Fetch existing VPC
data "aws_vpc" "existing" {
tags = {
Name = "production-vpc"
}
}
\\\`
Complete AWS VPC Example
\\\`hcl
VPC
resource "aws_vpc" "main" {
cidr_block = "10.0.0.0/16"
enable_dns_hostnames = true
tags = { Name = "main-vpc" }
}
Internet Gateway
resource "aws_internet_gateway" "main" {
vpc_id = aws_vpc.main.id
tags = { Name = "main-igw" }
}
Public Subnets (2 AZs)
resource "aws_subnet" "public" {
count = 2
vpc_id = aws_vpc.main.id
cidr_block = "10.0.${count.index}.0/24"
availability_zone = data.aws_availability_zones.available.names[count.index]
map_public_ip_on_launch = true
tags = { Name = "public-subnet-${count.index + 1}" }
}
Private Subnets (2 AZs)
resource "aws_subnet" "private" {
count = 2
vpc_id = aws_vpc.main.id
cidr_block = "10.0.${count.index + 10}.0/24"
availability_zone = data.aws_availability_zones.available.names[count.index]
tags = { Name = "private-subnet-${count.index + 1}" }
}
NAT Gateway (allows private subnets to reach internet)
resource "aws_eip" "nat" {
count = 1
domain = "vpc"
}
resource "aws_nat_gateway" "main" {
allocation_id = aws_eip.nat[0].id
subnet_id = aws_subnet.public[0].id
depends_on = [aws_internet_gateway.main]
tags = { Name = "main-nat-gw" }
}
Route Tables
resource "aws_route_table" "public" {
vpc_id = aws_vpc.main.id
route {
cidr_block = "0.0.0.0/0"
gateway_id = aws_internet_gateway.main.id
}
tags = { Name = "public-rt" }
}
resource "aws_route_table_association" "public" {
count = 2
subnet_id = aws_subnet.public[count.index].id
route_table_id = aws_route_table.public.id
}
data "aws_availability_zones" "available" {
state = "available"
}
\\\`
Terraform Commands
\\\`bash
terraform init # Initialize, download providers
terraform init -upgrade # Upgrade providers
terraform validate # Check syntax
terraform fmt # Format code
terraform fmt -recursive # Format all .tf files
terraform plan # Preview changes
terraform plan -out=tfplan # Save plan to file
terraform apply # Apply changes
terraform apply tfplan # Apply saved plan
terraform apply -auto-approve # Skip confirmation (CI/CD)
terraform destroy # Destroy all resources
terraform destroy -target=aws_instance.web # Destroy specific
terraform state list # List resources in state
terraform state show aws_instance.web # Show resource state
terraform state rm resource.name # Remove from state
terraform import aws_s3_bucket.main my-bucket # Import existing
terraform output # Show all outputs
terraform output vpc_id # Show specific output
terraform refresh # Sync state with real infra
\\\`