my-terraform

Terraform Comprehensive Cheatsheet (AWS-Focused)

This cheatsheet is a practical + reference-style guide to Terraform, with emphasis on AWS deployments. It covers syntax, workflow, core concepts, and links to official documentation for deeper study.

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1. What Terraform Is

Terraform is an Infrastructure as Code (IaC) tool by HashiCorp that lets you:

• Declare infrastructure in HCL (HashiCorp Configuration Language)
• Version-control infrastructure
• Provision, update, and destroy resources safely

Official Docs: https://developer.hashicorp.com/terraform/docs

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2. Terraform Core Concepts

2.1 Providers

Providers are plugins that talk to APIs (AWS, Azure, GCP, etc.).

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

AWS Provider Docs: https://registry.terraform.io/providers/hashicorp/aws/latest/docs

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2.2 Resources

Resources are infrastructure objects (EC2, VPC, ECS, S3, IAM, etc.).

resource "aws_s3_bucket" "example" {
  bucket = "my-bucket"
}

Resource Docs: https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources

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2.3 Data Sources

Used to read existing infrastructure.

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

Data Source Docs: https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources

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2.4 State

Terraform keeps a state file that maps configuration → real resources.

• Default: terraform.tfstate (local)
• Production: remote backend (S3 + DynamoDB)

State Docs: https://developer.hashicorp.com/terraform/language/state

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3. Terraform File Structure

Typical project layout:

.
├── main.tf          # Core resources
├── variables.tf     # Input variables
├── outputs.tf       # Outputs
├── providers.tf     # Provider config
├── versions.tf      # Terraform/provider versions
├── terraform.tfvars # Variable values

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4. Terraform Language (HCL) Syntax

4.1 Blocks

block_type "label1" "label2" {
  argument = value
}

---

4.2 Arguments

instance_type = "t3.micro"
count         = 2
enabled       = true

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4.3 Expressions

name = "${var.env}-app"

Expression Docs: https://developer.hashicorp.com/terraform/language/expressions

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4.4 Variables

Declare

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

Use

region = var.region

Variable Docs: https://developer.hashicorp.com/terraform/language/values/variables

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4.5 Outputs

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

Output Docs: https://developer.hashicorp.com/terraform/language/values/outputs

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4.6 Locals

locals {
  app_name = "my-app"
}

Local Docs: https://developer.hashicorp.com/terraform/language/values/locals

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5. Terraform Workflow (Terminal Commands)

5.1 Initialize Project

terraform init

• Downloads providers
• Configures backend

Docs: https://developer.hashicorp.com/terraform/cli/commands/init

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5.2 Validate Configuration

terraform validate

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5.3 Format Code

terraform fmt

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5.4 Plan Changes

terraform plan

With variables:

terraform plan -var-file=terraform.tfvars

Docs: https://developer.hashicorp.com/terraform/cli/commands/plan

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5.5 Apply Infrastructure

terraform apply

Auto-approve:

terraform apply -auto-approve

Docs: https://developer.hashicorp.com/terraform/cli/commands/apply

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5.6 Destroy Infrastructure

terraform destroy

Docs: https://developer.hashicorp.com/terraform/cli/commands/destroy

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6. AWS Authentication Methods

Terraform uses the AWS SDK.

Supported Methods

• AWS CLI credentials (~/.aws/credentials)
• Environment variables
• IAM roles (EC2, ECS, EKS)
• OIDC (GitHub Actions)

Auth Docs: https://registry.terraform.io/providers/hashicorp/aws/latest/docs#authentication

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7. AWS Core Resources (Most Used)

7.1 VPC

resource "aws_vpc" "main" {
  cidr_block = "10.0.0.0/16"
}

Docs: https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/vpc

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7.2 Subnets

resource "aws_subnet" "public" {
  vpc_id     = aws_vpc.main.id
  cidr_block = "10.0.1.0/24"
}

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7.3 EC2

resource "aws_instance" "web" {
  ami           = "ami-0abcdef"
  instance_type = "t3.micro"
}

Docs: https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/instance

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7.4 IAM Role

resource "aws_iam_role" "ecs_role" {
  name = "ecsTaskExecutionRole"

  assume_role_policy = jsonencode({
    Version = "2012-10-17"
    Statement = [{
      Effect = "Allow"
      Principal = { Service = "ecs-tasks.amazonaws.com" }
      Action = "sts:AssumeRole"
    }]
  })
}

Docs: https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/iam_role

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7.5 ECR

resource "aws_ecr_repository" "repo" {
  name = "my-app"
}

Docs: https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/ecr_repository

---

7.6 ECS Cluster

resource "aws_ecs_cluster" "cluster" {
  name = "my-cluster"
}

Docs: https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/ecs_cluster

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8. Modules (Reusable Infrastructure)

8.1 Module Structure

modules/vpc/
├── main.tf
├── variables.tf
├── outputs.tf

8.2 Use Module

module "vpc" {
  source = "./modules/vpc"
  cidr   = "10.0.0.0/16"
}

Module Docs: https://developer.hashicorp.com/terraform/language/modules

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9. Backends (Remote State for AWS)

S3 Backend (Recommended)

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

Backend Docs: https://developer.hashicorp.com/terraform/language/settings/backends/s3

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10. Meta-Arguments

count

count = 3

for_each

for_each = toset(["a", "b", "c"])

depends_on

depends_on = [aws_iam_role.ecs_role]

Docs: https://developer.hashicorp.com/terraform/language/meta-arguments

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11. Lifecycle Rules

lifecycle {
  prevent_destroy = true
  create_before_destroy = true
}

Docs: https://developer.hashicorp.com/terraform/language/meta-arguments/lifecycle

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12. Workspaces (Multiple Environments)

terraform workspace new dev
terraform workspace select prod

Docs: https://developer.hashicorp.com/terraform/cli/workspaces

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13. Best Practices (AWS)

• Use remote state (S3 + DynamoDB)
• Use IAM roles, not access keys
• Keep modules small & reusable
• Never commit .tfstate
• Use terraform plan in CI

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14. Official References (Bookmark These)

• Terraform Language: https://developer.hashicorp.com/terraform/language
• AWS Provider: https://registry.terraform.io/providers/hashicorp/aws/latest/docs
• Terraform CLI: https://developer.hashicorp.com/terraform/cli
• Registry Modules: https://registry.terraform.io/

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15. Next Logical Steps

• ECS Fargate deployment
• EKS cluster with Terraform
• CI/CD with GitHub Actions + Terraform
• OIDC authentication

(You can ask for deep-dive cheatsheets on any of these.)