infra-as-code

What this skill does

# Infrastructure as Code

Define, deploy, and manage cloud infrastructure using declarative configuration. Covers Terraform (multi-cloud), AWS CloudFormation, and Pulumi (code-first), with patterns for compute, networking, storage, databases, and state management.

## When to Use

- Setting up cloud infrastructure (VPCs, EC2, Lambda, S3, RDS, etc.)
- Writing or modifying Terraform configurations
- Managing Terraform state (remote backends, workspaces, imports)
- Creating CloudFormation templates
- Using Pulumi for infrastructure in TypeScript/Python/Go
- Planning and previewing infrastructure changes safely
- Debugging drift between declared state and actual resources
- Setting up multi-environment deployments (dev/staging/prod)

## Terraform

### Quick Start

```bash
# Install: https://developer.hashicorp.com/terraform/install

# Initialize a project
mkdir infra && cd infra
terraform init

# Core workflow
terraform plan        # Preview changes (safe, read-only)
terraform apply       # Apply changes (creates/modifies resources)
terraform destroy     # Tear down all resources

# Format and validate
terraform fmt -recursive    # Auto-format all .tf files
terraform validate          # Check syntax and config validity
```

### Project Structure

```
infra/
  main.tf              # Primary resources
  variables.tf         # Input variable declarations
  outputs.tf           # Output values
  providers.tf         # Provider configuration
  terraform.tfvars     # Variable values (don't commit secrets)
  backend.tf           # Remote state configuration
  modules/
    vpc/
      main.tf
      variables.tf
      outputs.tf
    compute/
      main.tf
      variables.tf
      outputs.tf
```

### Provider Configuration

```hcl
# providers.tf
terraform {
  required_version = ">= 1.5"
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 5.0"
    }
  }
}

provider "aws" {
  region = var.aws_region

  default_tags {
    tags = {
      Project     = var.project_name
      Environment = var.environment
      ManagedBy   = "terraform"
    }
  }
}
```

### Variables and Outputs

```hcl
# variables.tf
variable "aws_region" {
  type        = string
  default     = "us-east-1"
  description = "AWS region for all resources"
}

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

variable "instance_type" {
  type    = string
  default = "t3.micro"
}

variable "db_password" {
  type      = string
  sensitive = true
  description = "Database password (pass via TF_VAR_db_password env var)"
}

# outputs.tf
output "vpc_id" {
  value       = aws_vpc.main.id
  description = "VPC ID"
}

output "api_endpoint" {
  value = aws_lb.api.dns_name
}
```

### VPC + Networking

```hcl
# Networking module
resource "aws_vpc" "main" {
  cidr_block           = "10.0.0.0/16"
  enable_dns_support   = true
  enable_dns_hostnames = true

  tags = { Name = "${var.project_name}-vpc" }
}

resource "aws_subnet" "public" {
  count             = 2
  vpc_id            = aws_vpc.main.id
  cidr_block        = "10.0.${count.index + 1}.0/24"
  availability_zone = data.aws_availability_zones.available.names[count.index]

  map_public_ip_on_launch = true
  tags = { Name = "${var.project_name}-public-${count.index + 1}" }
}

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 = "${var.project_name}-private-${count.index + 1}" }
}

resource "aws_internet_gateway" "main" {
  vpc_id = aws_vpc.main.id
}

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
  }
}

resource "aws_route_table_association" "public" {
  count          = 2
  subnet_id      = aws_subnet.public[count.index].id
  route_table_id = aws_route_table.public.id
}

resource "aws_security_group" "web" {
  name_prefix = "${var.project_name}-web-"
  vpc_id      = aws_vpc.main.id

  ingress {
    from_port   = 80
    to_port     = 80
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  ingress {
    from_port   = 443
    to_port     = 443
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]
  }

  egress {
    from_port   = 0
    to_port     = 0
    protocol    = "-1"
    cidr_blocks = ["0.0.0.0/0"]
  }
}

data "aws_availability_zones" "available" {
  state = "available"
}
```

### Compute (EC2)

```hcl
resource "aws_instance" "app" {
  ami                    = data.aws_ami.ubuntu.id
  instance_type          = var.instance_type
  subnet_id              = aws_subnet.public[0].id
  vpc_security_group_ids = [aws_security_group.web.id]
  key_name               = var.key_pair_name

  user_data = <<-EOF
    #!/bin/bash
    apt-get update
    apt-get install -y docker.io
    systemctl start docker
    docker run -d -p 80:8080 ${var.docker_image}
  EOF

  tags = { Name = "${var.project_name}-app" }
}

data "aws_ami" "ubuntu" {
  most_recent = true
  owners      = ["099720109477"] # Canonical

  filter {
    name   = "name"
    values = ["ubuntu/images/hvm-ssd/ubuntu-*-24.04-amd64-server-*"]
  }
}
```

### S3 + Static Website

```hcl
resource "aws_s3_bucket" "website" {
  bucket = "${var.project_name}-website"
}

resource "aws_s3_bucket_website_configuration" "website" {
  bucket = aws_s3_bucket.website.id

  index_document { suffix = "index.html" }
  error_document { key = "error.html" }
}

resource "aws_s3_bucket_public_access_block" "website" {
  bucket = aws_s3_bucket.website.id

  block_public_acls       = false
  block_public_policy     = false
  ignore_public_acls      = false
  restrict_public_buckets = false
}

resource "aws_s3_bucket_policy" "website" {
  bucket = aws_s3_bucket.website.id

  policy = jsonencode({
    Version = "2012-10-17"
    Statement = [{
      Sid       = "PublicRead"
      Effect    = "Allow"
      Principal = "*"
      Action    = "s3:GetObject"
      Resource  = "${aws_s3_bucket.website.arn}/*"
    }]
  })

  depends_on = [aws_s3_bucket_public_access_block.website]
}
```

### RDS Database

```hcl
resource "aws_db_subnet_group" "main" {
  name       = "${var.project_name}-db"
  subnet_ids = aws_subnet.private[*].id
}

resource "aws_security_group" "db" {
  name_prefix = "${var.project_name}-db-"
  vpc_id      = aws_vpc.main.id

  ingress {
    from_port       = 5432
    to_port         = 5432
    protocol        = "tcp"
    security_groups = [aws_security_group.web.id]
  }
}

resource "aws_db_instance" "main" {
  identifier        = "${var.project_name}-db"
  engine            = "postgres"
  engine_version    = "16.1"
  instance_class    = "db.t3.micro"
  allocated_storage = 20

  db_name  = var.db_name
  username = var.db_username
  password = var.db_password

  db_subnet_group_name   = aws_db_subnet_group.main.name
  vpc_security_group_ids = [aws_security_group.db.id]

  backup_retention_period = 7
  skip_final_snapshot     = var.environment != "prod"
  deletion_protection     = var.environment == "prod"
}
```

### Lambda Function

```hcl
data "archive_file" "lambda_zip" {
  type        = "zip"
  source_dir  = "${path.module}/lambda"
  output_path = "${path.module}/lambda.zip"
}

resource "aws_lambda_function" "api" {
  function_name    = "${var.project_name}-api"
  filename         = data.archive_file.lambda_zip.output_path
  source_code_hash = data.archive_file.lambda_zip.output_base64sha256
  handler          = "index.handler"
  runtime          = "nodejs20.x"
  timeout          = 30

  role = aws_iam_role.lambda_exec.arn

  environment {
    variables = {
      DB_HOST     = aws_db_instance.main.endpoint
      ENVIRONMENT = var.environment
    }
  }
}

resource "aws_iam_role" "lambda_exec" {
  na