terraform

name	terraform
description	Use when writing Terraform configurations for multi-cloud infrastructure. Covers HCL resources, modules, state management, providers, and plan/apply workflow. USE FOR: multi-cloud provisioning, HCL configuration, Terraform state management, provider modules, plan/apply workflow DO NOT USE FOR: imperative infrastructure code (use pulumi), Azure-only deployments (use bicep), AWS-only stacks (use cloud-formation)
license	MIT
metadata	{"displayName":"Terraform","author":"Tyler-R-Kendrick"}
compatibility	claude, copilot, cursor
references	[{"title":"Terraform Documentation","url":"https://developer.hashicorp.com/terraform/docs"},{"title":"Terraform GitHub Repository","url":"https://github.com/hashicorp/terraform"},{"title":"Terraform Registry","url":"https://registry.terraform.io"}]

Terraform

Overview

Terraform is HashiCorp's open-source IaC tool for provisioning infrastructure across any cloud provider using HCL (HashiCorp Configuration Language). It uses a plan/apply workflow with state tracking to manage resource lifecycles declaratively.

Basic Configuration

terraform {
  required_version = ">= 1.9"
  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
}

variable "region" {
  type    = string
  default = "us-east-1"
}

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

resource "aws_s3_bucket" "assets" {
  bucket = "my-app-${var.environment}-assets"
  tags = {
    Environment = var.environment
  }
}

resource "aws_s3_bucket_versioning" "assets" {
  bucket = aws_s3_bucket.assets.id
  versioning_configuration {
    status = "Enabled"
  }
}

output "bucket_arn" {
  value = aws_s3_bucket.assets.arn
}

Workflow

# Initialize providers and backend
terraform init

# Preview changes
terraform plan -var="environment=prod"

# Apply changes
terraform apply -var="environment=prod"

# Destroy resources
terraform destroy -var="environment=prod"

Modules

# modules/vpc/main.tf
variable "cidr_block" { type = string }
variable "name" { type = string }

resource "aws_vpc" "this" {
  cidr_block = var.cidr_block
  tags       = { Name = var.name }
}

output "vpc_id" { value = aws_vpc.this.id }

# main.tf
module "vpc" {
  source     = "./modules/vpc"
  cidr_block = "10.0.0.0/16"
  name       = "my-vpc-${var.environment}"
}

State Management

Backend	Use Case
s3 + DynamoDB	AWS (state in S3, locking in DynamoDB)
azurerm	Azure (state in Blob Storage)
gcs	GCP (state in Cloud Storage)
Terraform Cloud	Managed state with collaboration features

Key HCL Features

Feature	Example
for_each	for_each = toset(["a", "b"])
count	count = var.create ? 1 : 0
dynamic blocks	Generate repeated nested blocks
locals	locals { name = "${var.app}-${var.env}" }
Data sources	data "aws_ami" "latest" { ... }
depends_on	Explicit dependency ordering
lifecycle	prevent_destroy, ignore_changes, replace_triggered_by

Best Practices

• Always run terraform plan before apply and review the diff.
• Use remote state with locking (S3 + DynamoDB, Terraform Cloud) for team collaboration.
• Pin provider versions with ~> constraints to avoid breaking changes.
• Use modules for reusable infrastructure patterns.
• Use terraform fmt and terraform validate in CI.
• Never store secrets in .tf files — use variables with environment variables or a secrets manager.
• Use lifecycle { prevent_destroy = true } on critical stateful resources.
• Use workspaces or directory structure for environment separation (dev/staging/prod).