terraform git:20260516.215750bA

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---
description: Terraform module and resource generation rules — blast radius, IAM least privilege, SOC 2 defaults
globs: ["**/*.tf", "**/*.tfvars"]
alwaysApply: false
---

# Terraform Rules

## Module structure

Every Terraform module must have: `main.tf`, `variables.tf`, `outputs.tf`, `versions.tf`, `README.md`.

## Variable validation — always include

```hcl
variable "environment" {
  type = string
  validation {
    condition     = contains(["dev", "staging", "production"], var.environment)
    error_message = "environment must be dev, staging, or production"
  }
}
```

## Pipeline order — enforce all gates before plan

`terraform fmt -check` → `terraform validate` → `tflint` → `checkov`/`tfsec` → `plan`

## IAM — never generate wildcards

```hcl
# ❌ Never
statement {
  actions   = ["*"]
  resources = ["*"]
}

# ✅ Always
statement {
  actions   = ["s3:GetObject", "s3:ListBucket"]
  resources = ["arn:aws:s3:::my-bucket", "arn:aws:s3:::my-bucket/*"]
}
```

## Tagging — always enforce at provider level

```hcl
provider "aws" {
  default_tags {
    tags = { env = var.environment, team = var.team, managed-by = "terraform" }
  }
}
```

## SOC 2 — never generate

- `publicly_accessible = true` on RDS, Redshift, OpenSearch
- `encrypted = false` on any storage (S3, EBS, RDS, DynamoDB, ElastiCache, EFS)
- `is_multi_region_trail = false` on CloudTrail
- `enable_log_file_validation = false` on CloudTrail
- `skip_final_snapshot = true` on production databases
- `deletion_protection = false` on production databases
- `enable = false` on GuardDuty
- `:latest` image tags in any resource

## SOC 2 — always generate on data resources

```hcl
resource "aws_kms_key" "..." {
  enable_key_rotation     = true   # CC6.7
  deletion_window_in_days = 30
}

resource "aws_cloudtrail" "..." {
  is_multi_region_trail      = true   # CC7.2
  enable_log_file_validation = true
  kms_key_id                 = aws_kms_key.cloudtrail.arn
}

resource "aws_db_instance" "..." {
  storage_encrypted       = true
  backup_retention_period = 35    # A1.2
  deletion_protection     = true
  skip_final_snapshot     = false
  multi_az                = true
}
```

## State backend — always encrypt

```hcl
terraform {
  backend "s3" {
    encrypt        = true
    kms_key_id     = var.kms_key_arn
    dynamodb_table = "terraform-state-lock"
  }
}
```

## Blast radius note

Before every destructive operation, state:
- What gets replaced (forces new resource)
- What downstream resources depend on it
- Mid-apply failure impact
- Rollback path