Terraform

Infrastructure as Code with Terraform.

When to Use

• Creating infrastructure modules

• Managing Terraform state

• Multi-environment deployments

• Importing existing resources

• Troubleshooting drift

Module Structure

modules/ └── vpc/ ├── main.tf # Resources ├── variables.tf # Input variables ├── outputs.tf # Output values └── versions.tf # Provider requirements

Best Practices

Variables

variable "environment" { description = "Environment name" type = string validation { condition = contains(["dev", "staging", "prod"], var.environment) error_message = "Environment must be dev, staging, or prod." } }

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

Resources

resource "aws_instance" "main" { ami = data.aws_ami.latest.id instance_type = var.instance_type

tags = merge(var.tags, { Name = "${var.project}-${var.environment}" })

lifecycle { create_before_destroy = true } }

Outputs

output "instance_id" { description = "EC2 instance ID" value = aws_instance.main.id }

State Management

backend.tf

terraform { backend "s3" { bucket = "terraform-state-bucket" key = "project/terraform.tfstate" region = "us-east-1" encrypt = true dynamodb_table = "terraform-locks" } }

Common Commands

Initialize and plan

terraform init terraform plan -out=tfplan

Apply with auto-approve (CI/CD)

terraform apply -auto-approve tfplan

Import existing resource

terraform import aws_instance.main i-1234567890abcdef0

State operations

terraform state list terraform state show aws_instance.main terraform state mv aws_instance.old aws_instance.new

Workspace Strategy

Create workspaces per environment

terraform workspace new dev terraform workspace new prod

Use in configuration

locals { env_config = { dev = { instance_type = "t3.micro" } prod = { instance_type = "t3.large" } } config = local.env_config[terraform.workspace] }

Examples

Input: "Create a VPC module" Action: Create module with subnets, route tables, NAT gateway, proper outputs

Input: "Fix state drift" Action: Run plan, identify drift, decide refresh vs import vs manual fix