terraform-aws

What this skill does

# Terraform AWS Skill

Production patterns for AWS infrastructure provisioning with security and cost optimization.

## Provider Setup

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

provider "aws" {
  region = var.aws_region

  default_tags {
    tags = {
      Environment = var.environment
      Project     = var.project
      ManagedBy   = "Terraform"
    }
  }
}
```

## VPC Architecture

### Multi-AZ VPC
```hcl
module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "5.1.2"

  name = "${var.project}-vpc"
  cidr = "10.0.0.0/16"

  azs             = ["us-east-1a", "us-east-1b", "us-east-1c"]
  private_subnets = ["10.0.1.0/24", "10.0.2.0/24", "10.0.3.0/24"]
  public_subnets  = ["10.0.101.0/24", "10.0.102.0/24", "10.0.103.0/24"]

  enable_nat_gateway     = true
  single_nat_gateway     = var.environment != "prod"
  one_nat_gateway_per_az = var.environment == "prod"

  enable_dns_hostnames = true
  enable_flow_log      = true
}
```

### Security Groups
```hcl
resource "aws_security_group" "web" {
  name_prefix = "${var.project}-web-"
  vpc_id      = module.vpc.vpc_id

  lifecycle {
    create_before_destroy = true
  }
}

resource "aws_vpc_security_group_ingress_rule" "https" {
  security_group_id = aws_security_group.web.id
  from_port         = 443
  to_port           = 443
  ip_protocol       = "tcp"
  cidr_ipv4         = "0.0.0.0/0"
}
```

## EC2 Instances

### Launch Template + ASG
```hcl
resource "aws_launch_template" "app" {
  name_prefix   = "${var.project}-"
  image_id      = data.aws_ami.amazon_linux.id
  instance_type = var.instance_type

  metadata_options {
    http_tokens = "required"  # IMDSv2
  }

  block_device_mappings {
    device_name = "/dev/xvda"
    ebs {
      volume_size = 20
      volume_type = "gp3"
      encrypted   = true
    }
  }

  iam_instance_profile {
    arn = aws_iam_instance_profile.app.arn
  }
}

resource "aws_autoscaling_group" "app" {
  name                = "${var.project}-asg"
  desired_capacity    = 2
  max_size            = 10
  min_size            = 1
  vpc_zone_identifier = module.vpc.private_subnets
  target_group_arns   = [aws_lb_target_group.app.arn]

  launch_template {
    id      = aws_launch_template.app.id
    version = "$Latest"
  }

  instance_refresh {
    strategy = "Rolling"
    preferences {
      min_healthy_percentage = 75
    }
  }
}
```

## IAM Best Practices

### Least Privilege Role
```hcl
data "aws_iam_policy_document" "assume" {
  statement {
    effect = "Allow"
    principals {
      type        = "Service"
      identifiers = ["ec2.amazonaws.com"]
    }
    actions = ["sts:AssumeRole"]
  }
}

resource "aws_iam_role" "app" {
  name               = "${var.project}-app"
  assume_role_policy = data.aws_iam_policy_document.assume.json
}

data "aws_iam_policy_document" "app" {
  statement {
    effect = "Allow"
    actions = [
      "s3:GetObject",
      "s3:PutObject"
    ]
    resources = ["${aws_s3_bucket.app.arn}/*"]
  }
}

resource "aws_iam_role_policy" "app" {
  name   = "app-policy"
  role   = aws_iam_role.app.id
  policy = data.aws_iam_policy_document.app.json
}
```

## RDS Database

```hcl
resource "aws_db_instance" "main" {
  identifier     = "${var.project}-db"
  engine         = "postgres"
  engine_version = "15.4"
  instance_class = "db.t3.medium"

  allocated_storage     = 100
  max_allocated_storage = 500
  storage_encrypted     = true

  db_name  = var.db_name
  username = var.db_username
  password = random_password.db.result

  multi_az               = var.environment == "prod"
  db_subnet_group_name   = aws_db_subnet_group.main.name
  vpc_security_group_ids = [aws_security_group.rds.id]

  backup_retention_period = 30
  deletion_protection     = var.environment == "prod"
  skip_final_snapshot     = var.environment != "prod"

  performance_insights_enabled = true
}
```

## S3 Bucket

```hcl
resource "aws_s3_bucket" "app" {
  bucket = "${var.project}-${var.environment}-data"
}

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

resource "aws_s3_bucket_server_side_encryption_configuration" "app" {
  bucket = aws_s3_bucket.app.id

  rule {
    apply_server_side_encryption_by_default {
      sse_algorithm     = "aws:kms"
      kms_master_key_id = aws_kms_key.main.arn
    }
  }
}

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

  block_public_acls       = true
  block_public_policy     = true
  ignore_public_acls      = true
  restrict_public_buckets = true
}
```

## Troubleshooting

| Error | Cause | Solution |
|-------|-------|----------|
| `UnauthorizedAccess` | Missing IAM permissions | Check role policies |
| `VPCIdNotSpecified` | VPC not provided | Set vpc_id explicitly |
| `ResourceInUse` | Dependencies exist | Check dependents first |
| `LimitExceeded` | Quota reached | Request limit increase |

## Usage

```python
Skill("terraform-aws")
```

## Related

- **Agent**: 04-terraform-aws (PRIMARY_BOND)