Policy as Code

Overview

Policy as Code validates infrastructure changes against security, compliance, and organizational rules before deployment. This prevents misconfigurations from reaching production.

graph LR
    A[terraform plan] --> B[terraform show -json]
    B --> C[conftest test]
    C --> D{Pass?}
    D -->|Yes| E[terraform apply]
    D -->|No| F[Fail Pipeline]
    
    style F fill:#ff6b6b
    style E fill:#90EE90

Policy Tools

Tool	Language	Use Case
OPA/Conftest	Rego	Custom policies, Terraform
Checkov	Python/YAML	Security scanning, compliance
tfsec	Go	Terraform security
SCPs	JSON	AWS Organizations guardrails

Best Practices

1. Fail early - Run policies in CI before plan
2. Version policies - Treat as code, review changes
3. Start permissive - Warn first, then enforce
4. Document exceptions - Clear process for bypasses
5. Layer policies - OPA for custom, Checkov for security
6. Test policies - Unit tests for Rego rules

---

Example 1: OPA/Conftest Policies for Terraform

Custom policies to enforce tagging, encryption, and access controls.

📁 Location: policies/conftest/

Sample Policies

# policies/terraform/required_tags.rego
package terraform.required_tags

required_tags := ["Environment", "Owner", "Project", "CostCenter"]

deny[msg] {
  resource := input.resource_changes[_]
  resource.change.actions[_] == "create"
  
  # Check for required tags
  missing := required_tags - object.keys(resource.change.after.tags)
  count(missing) > 0
  
  msg := sprintf(
    "%s '%s' is missing required tags: %v",
    [resource.type, resource.name, missing]
  )
}

# policies/terraform/s3_encryption.rego
package terraform.s3_security

deny[msg] {
  resource := input.resource_changes[_]
  resource.type == "aws_s3_bucket"
  resource.change.actions[_] == "create"
  
  # Check for encryption
  not resource.change.after.server_side_encryption_configuration
  
  msg := sprintf("S3 bucket '%s' must have encryption enabled", [resource.name])
}

deny[msg] {
  resource := input.resource_changes[_]
  resource.type == "aws_s3_bucket"
  resource.change.actions[_] == "create"
  
  # Check for public access block
  not resource.change.after.block_public_acls
  
  msg := sprintf("S3 bucket '%s' must block public access", [resource.name])
}

Running Policies

# Generate plan JSON
terraform plan -out=tfplan
terraform show -json tfplan > tfplan.json

# Run Conftest
conftest test tfplan.json -p policies/terraform/

---

Example 2: Checkov for Security Scanning

Pre-built security checks with custom policies.

📁 Location: policies/checkov/

Running Checkov

# Scan Terraform files
checkov -d terraform/ --framework terraform

# With custom policies
checkov -d terraform/ --external-checks-dir policies/checkov/

# Output for CI
checkov -d terraform/ -o junitxml > checkov-results.xml

Custom Checkov Policy

# policies/checkov/custom_rds_encryption.yaml
metadata:
  id: "CUSTOM_RDS_001"
  name: "Ensure RDS instances are encrypted"
  category: "ENCRYPTION"
  
definition:
  cond_type: "attribute"
  resource_types:
    - "aws_db_instance"
  attribute: "storage_encrypted"
  operator: "is_true"

---

CI Integration

# GitHub Actions example
- name: Terraform Plan
  run: |
    terraform plan -out=tfplan
    terraform show -json tfplan > tfplan.json

- name: Run Conftest
  run: conftest test tfplan.json -p policies/ --no-fail

- name: Run Checkov
  uses: bridgecrewio/checkov-action@master
  with:
    directory: terraform/
    framework: terraform
    soft_fail: false

---

Validation Checklist

• OPA/Conftest policies for custom rules
• Checkov for security baseline
• Policies run in CI before apply
• Policy exceptions documented
• Policies version controlled
• Policy test coverage

Related Skills

• Compliance Tagging - Tag policies
• GitOps Workflow - CI integration
• IAM Least Privilege - IAM policies