Terraform Reviewer

Terraform Reviewer Skill

Purpose

Reviews Terraform code for module structure, state management, security, and best practices.

When to Use

• Terraform code review
• Module structure review
• State backend configuration
• Security policy review
• Variable and output review

Project Detection

• *.tf files in project
• main.tf, variables.tf, outputs.tf
• modules/ directory
• terraform.tfvars

Workflow

Step 1: Analyze Project

**Terraform**: 1.6+
**Provider**: AWS/GCP/Azure
**Backend**: S3/GCS/Azure Blob
**Modules**: Custom + Registry

Step 2: Select Review Areas

AskUserQuestion:

"Which areas to review?"
Options:
- Full Terraform review (recommended)
- Module structure
- State management
- Security and compliance
- Variable validation
multiSelect: true

Detection Rules

Module Structure

# GOOD: Project structure
terraform/
├── environments/
│   ├── dev/
│   │   ├── main.tf
│   │   ├── variables.tf
│   │   └── terraform.tfvars
│   └── prod/
│       ├── main.tf
│       ├── variables.tf
│       └── terraform.tfvars
├── modules/
│   ├── vpc/
│   │   ├── main.tf
│   │   ├── variables.tf
│   │   └── outputs.tf
│   └── eks/
│       ├── main.tf
│       ├── variables.tf
│       └── outputs.tf
└── README.md

# BAD: Hardcoded values
resource "aws_instance" "web" {
  ami           = "ami-12345678"
  instance_type = "t3.micro"

  tags = {
    Name = "web-server"
  }
}

# GOOD: Parameterized with variables
variable "instance_type" {
  description = "EC2 instance type"
  type        = string
  default     = "t3.micro"

  validation {
    condition     = can(regex("^t3\\.", var.instance_type))
    error_message = "Instance type must be t3 family."
  }
}

variable "environment" {
  description = "Environment name"
  type        = string

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

resource "aws_instance" "web" {
  ami           = data.aws_ami.amazon_linux.id
  instance_type = var.instance_type

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

State Management

# BAD: Local state (default)
# No backend configuration

# GOOD: Remote backend with locking
terraform {
  backend "s3" {
    bucket         = "mycompany-terraform-state"
    key            = "prod/vpc/terraform.tfstate"
    region         = "us-east-1"
    encrypt        = true
    dynamodb_table = "terraform-state-lock"
  }
}

# For GCP
terraform {
  backend "gcs" {
    bucket  = "mycompany-terraform-state"
    prefix  = "prod/vpc"
  }
}

Security

# BAD: Security issues
resource "aws_security_group" "web" {
  ingress {
    from_port   = 0
    to_port     = 65535
    protocol    = "tcp"
    cidr_blocks = ["0.0.0.0/0"]  # Wide open!
  }
}

resource "aws_s3_bucket" "data" {
  bucket = "my-data-bucket"
  acl    = "public-read"  # Public!
}

# GOOD: Secure configuration
resource "aws_security_group" "web" {
  name        = "${var.project}-web-sg"
  description = "Security group for web servers"
  vpc_id      = var.vpc_id

  ingress {
    description = "HTTPS from load balancer"
    from_port   = 443
    to_port     = 443
    protocol    = "tcp"
    security_groups = [aws_security_group.alb.id]
  }

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

  tags = local.common_tags
}

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

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

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

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

  rule {
    apply_server_side_encryption_by_default {
      sse_algorithm     = "aws:kms"
      kms_master_key_id = aws_kms_key.s3.arn
    }
  }
}

Variable Validation

# GOOD: Well-defined variables
variable "vpc_cidr" {
  description = "CIDR block for VPC"
  type        = string
  default     = "10.0.0.0/16"

  validation {
    condition     = can(cidrnetmask(var.vpc_cidr))
    error_message = "Must be a valid CIDR block."
  }
}

variable "db_password" {
  description = "Database password"
  type        = string
  sensitive   = true  # Won't show in logs

  validation {
    condition     = length(var.db_password) >= 16
    error_message = "Password must be at least 16 characters."
  }
}

variable "allowed_environments" {
  description = "List of allowed environment names"
  type        = list(string)
  default     = ["dev", "staging", "prod"]
}

Resource Naming

# GOOD: Consistent naming and tagging
locals {
  name_prefix = "${var.project}-${var.environment}"

  common_tags = {
    Project     = var.project
    Environment = var.environment
    ManagedBy   = "terraform"
    Owner       = var.owner
  }
}

resource "aws_vpc" "main" {
  cidr_block = var.vpc_cidr

  tags = merge(local.common_tags, {
    Name = "${local.name_prefix}-vpc"
  })
}

Response Template

## Terraform Review Results

**Project**: [name]
**Terraform**: 1.6 | **Provider**: AWS

### Module Structure
| Status | File | Issue |
|--------|------|-------|
| MEDIUM | main.tf | 500+ lines, should split |

### State Management
| Status | File | Issue |
|--------|------|-------|
| CRITICAL | - | Using local state |

### Security
| Status | File | Issue |
|--------|------|-------|
| CRITICAL | security.tf:23 | Security group allows 0.0.0.0/0 |

### Variables
| Status | File | Issue |
|--------|------|-------|
| HIGH | variables.tf | db_password not marked sensitive |

### Recommended Actions
1. [ ] Configure remote state backend with locking
2. [ ] Restrict security group ingress rules
3. [ ] Mark sensitive variables
4. [ ] Split main.tf into logical files

Best Practices

1. Structure: Separate by environment, use modules
2. State: Remote backend with locking and encryption
3. Security: No secrets in code, least privilege
4. Variables: Type constraints, validation, descriptions
5. Naming: Consistent convention, standard tags

Integration

• k8s-reviewer: EKS/GKE cluster configs
• infra-security-reviewer: Compliance checks
• ci-cd-reviewer: Terraform in pipelines