Terraform Configuration

Writing and organizing Terraform infrastructure-as-code configurations.

Basic Structure

Provider configuration

terraform { required_version = ">= 1.0"

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

backend "s3" { bucket = "my-terraform-state" key = "prod/terraform.tfstate" region = "us-east-1" } }

provider "aws" { region = var.region }

Resources

resource "aws_instance" "web" { ami = var.ami_id instance_type = var.instance_type

tags = { Name = "web-server" Environment = var.environment }

lifecycle { create_before_destroy = true prevent_destroy = false } }

Variables

variable "environment" { description = "Environment name" type = string default = "development"

validation { condition = contains(["development", "staging", "production"], var.environment) error_message = "Environment must be development, staging, or production." } }

variable "instance_count" { description = "Number of instances" type = number default = 1 }

variable "tags" { description = "Resource tags" type = map(string) default = {} }

Outputs

output "instance_id" { description = "ID of the EC2 instance" value = aws_instance.web.id }

output "public_ip" { description = "Public IP address" value = aws_instance.web.public_ip sensitive = false }

Data Sources

data "aws_ami" "amazon_linux" { most_recent = true owners = ["amazon"]

filter { name = "name" values = ["amzn2-ami-hvm-*-x86_64-gp2"] } }

data "aws_vpc" "default" { default = true }

Locals

locals { common_tags = { Project = "myapp" ManagedBy = "terraform" Environment = var.environment }

name_prefix = "${var.project}-${var.environment}" }

resource "aws_instance" "web" {

...

tags = merge(local.common_tags, { Name = "${local.name_prefix}-web" }) }

Common Commands

Initialize

terraform init

Format

terraform fmt -recursive

Validate

terraform validate

Plan

terraform plan -out=tfplan

Apply

terraform apply tfplan

Destroy

terraform destroy

Show state

terraform show

List resources

terraform state list

Best Practices

File Organization

project/ ├── main.tf # Main resources ├── variables.tf # Variable declarations ├── outputs.tf # Output declarations ├── versions.tf # Provider versions ├── terraform.tfvars # Variable values (gitignored if sensitive) └── modules/ # Local modules └── network/

Use Variables for Flexibility

Bad

resource "aws_instance" "web" { instance_type = "t2.micro" }

Good

resource "aws_instance" "web" { instance_type = var.instance_type }

Use Locals for Computed Values

locals { timestamp = formatdate("YYYY-MM-DD-hhmmss", timestamp()) full_name = "${var.prefix}-${var.name}-${var.suffix}" }