By Sebastian Stadil —

Blog Series: Enforcing Policy as Code in Terraform (Part 5 of 5)

Best Practices, CI/CD Integration, and Culture

Welcome to the concluding installment of our 5-part series on Policy as Code (PaC) with Terraform!

  • In Part 1, we defined PaC and underscored its importance.
  • Part 2 looked at Terraform's native validation and the need for dedicated tools.
  • Part 3 explored the power of Open Policy Agent (OPA) and conftest.
  • Part 4 expanded our toolkit with HashiCorp Sentinel, tfsec, and Checkov.

Now, in Part 5, we'll synthesize what we've learned. We'll discuss best practices for integrating these PaC tools into your CI/CD pipelines, strategies for the lifecycle management of your policies, and, crucially, how to foster an organizational culture that truly embraces Policy as Code.

Weaving PaC into Your CI/CD Pipeline: The Automation Heartbeat

The real power of PaC is unleashed when it's an automated, integral part of your Continuous Integration/Continuous Deployment (CI/CD) pipeline. This is where policies transform from theoretical rules into active guardians of your infrastructure.

Key Enforcement Points in CI/CD:

  1. Pre-Commit (Local Development):
    • What: Integrate tools like TFLint, tfsec, or Checkov (and even conftest for local plan checks) into pre-commit hooks.
    • Why: Catch syntax errors, style issues, and basic misconfigurations before code is even pushed to the repository. This provides the fastest feedback loop to developers.
    • How: Use frameworks like pre-commit and collections like pre-commit-terraform to manage hooks for various tools.
  2. On Pull/Merge Request (CI Phase - Static Analysis):
    • What: As soon as a developer opens a pull request, trigger automated checks on the Terraform HCL code.
    • Why: Enforce coding standards and catch a wide range of static configuration issues before merging into the main branch.
    • How: Your CI server (GitHub Actions, GitLab CI, Jenkins, etc.) should run TFLint, tfsec, and Checkov (in HCL scanning mode). Results can be posted as PR comments or checks.
  3. After terraform plan (CI Phase - Plan-Time Validation):
    • What: This is a critical stage. After a successful terraform plan, convert the plan to JSON and evaluate it against your more complex organizational policies using OPA/conftest or Checkov (in plan scanning mode).
    • Why: Validates the intended state of your infrastructure, catching issues that require resolved values or inter-resource context.
    • How:
      • terraform plan -out=tfplan.binary
      • terraform show -json tfplan.binary > tfplan.json
      • conftest test --policy ./policies/ tfplan.json (or similar for Checkov).
      • The CI job fails if policy violations are found.
  4. Before terraform apply (CD Phase - Policy Gate):
    • What: The results from the plan-time validation act as a gate.
    • Why: Prevents the deployment of non-compliant infrastructure.
    • How: If mandatory policies failed in the previous step, the CI/CD pipeline halts and does not proceed to terraform apply. Advisory failures might log warnings but allow the pipeline to continue (perhaps requiring manual approval).

Example Snippet (Conceptual GitHub Action for tfsec):

name: Terraform Static Analysis
on: [pull_request]
jobs:
  tfsec:
    name: tfsec
    runs-on: ubuntu-latest
    steps:
      - name: Checkout code
        uses: actions/checkout@v3
      - name: Run tfsec
        uses: aquasecurity/tfsec-action@v1.0.0
        with:
          working_directory: ./your-terraform-code/

Terraform Cloud/Enterprise Integration: If you're using TFC/TFE, Sentinel and OPA policy checks are built into the run workflow, automatically occurring between the plan and apply stages. Policy Sets are linked to VCS repositories for a GitOps-style policy management experience.

The Policy Lifecycle: Treating Policies as Code

Effective PaC means treating your policies with the same rigor as your application or infrastructure code. This involves a well-defined lifecycle:

  1. Authoring:
    • Collaborate: Define policy requirements with security, compliance, operations, and development teams.
    • Document: Clearly document each policy's purpose, logic, and remediation steps.
    • Modularize: Write reusable policy functions or modules (e.g., in Rego or HSL).
  2. Testing (Crucial!):
    • Unit Tests: Test individual policy rules with mock data. OPA has opa test with _test.rego files; Sentinel has sentinel test with pass.json/fail.json scenarios.
    • Realistic Mock Data: Use representative tfplan.json snippets or configuration examples.
    • Automate Tests: Integrate policy tests into a CI pipeline for your policy repository. Every change to a policy should trigger its tests.
  3. Deployment & Versioning:
    • Git is King: Store all policy code, tests, and documentation in Git.
    • Semantic Versioning (SemVer): Use MAJOR.MINOR.PATCH for policy sets or shared libraries. Tag releases in Git.
    • Gradual Rollout: Introduce new policies in "advisory" or "audit" mode first. Observe their impact, fix false positives, and then escalate to "soft-mandatory" or "hard-mandatory" enforcement.
    • Automated Distribution: For OPA, consider OPA Bundles distributed via HTTP or tools like OPAL. For Sentinel in TFC/TFE, VCS integration handles updates.
  4. Maintenance & Review:
    • Continuous Improvement: Policies aren't static. Regularly review and update them based on new threats, compliance changes, cloud service updates, and feedback.
    • Monitor Performance: Ensure policies don't unduly slow down CI/CD pipelines.

Structuring Policy Repositories:

  • Organize policies logically (e.g., by tool, domain like security/, cost/, or cloud provider aws/s3/).
  • Co-locate tests with policies.
  • Use a clear README.md for the repository.

Handling Exceptions and False Positives Gracefully

  • False Positives: If a policy wrongly flags compliant resources, refine the policy logic.
  • Exceptions: Establish a formal, audited process for requesting, reviewing, approving, and documenting exceptions. Exceptions should be time-bound and regularly reviewed.
  • Suppressions: Some tools allow in-code suppressions (e.g., Checkov skip comments). Use these sparingly, with mandatory justification, and monitor their usage.

Cultivating a Policy as Code Culture

Technology is only half the battle. Successfully embedding PaC requires a cultural shift:

  1. Shared Responsibility (DevSecOps):
    • Security and compliance are not just the job of a central team but a responsibility shared by everyone involved in delivering infrastructure.
    • Developers should be empowered and educated to understand and address policy violations early.
  2. Collaboration is Key:
    • Break down silos between development, operations, security, and compliance teams.
    • Policy definition and refinement should be a collaborative effort to ensure policies are practical and effective.
  3. Education and Training:
    • Invest in training teams on the chosen PaC tools, policy languages (Rego, HSL, etc.), and the organization's specific policies.
    • Help them understand the "why" behind the policies, not just the "what."
  4. Start Small, Iterate, and Show Value:
    • Don't try to boil the ocean. Begin with a few high-impact policies that address clear pain points (e.g., critical security gaps, major cost concerns).
    • Demonstrate early wins to build momentum and buy-in.
    • Iterate on your policies and processes based on feedback and lessons learned.
  5. Feedback Loops:
    • Make it easy for developers to understand policy violations and how to fix them. Provide clear error messages and links to documentation.
    • Establish channels for developers to provide feedback on policies – are they too restrictive? Are there false positives?
  6. Leadership Buy-in:
    • Secure support from leadership for the PaC initiative. This helps drive adoption and allocate necessary resources.

The Future is Codified Governance

Policy as Code is more than just a set of tools; it's a transformative approach to governance in the cloud era. By codifying your rules, automating their enforcement, and fostering a culture of shared responsibility, you can build more secure, compliant, cost-effective, and reliable infrastructure with greater speed and confidence.

This series has equipped you with the foundational knowledge to embark on or enhance your Policy as Code journey with Terraform. The path involves continuous learning, adaptation, and collaboration, but the rewards – robust, automated governance – are well worth the effort.

Thank you for joining us on this series! We hope it has been insightful and empowers you to tame the complexities of modern cloud infrastructure with Policy as Code.