Policy as Code vs. IaC Security: What's the Difference?
Clarify the crucial distinctions between Policy-as-Code (PaC) and Infrastructure as Code (IaC) security scanning, and learn how they work together to create a robust cloud security posture.
What You'll Learn
🏷️ Topics Covered
The Modern Dilemma: Speed vs. Security
In the world of DevOps and Infrastructure as Code (IaC), we're deploying infrastructure faster than ever. But this speed introduces a challenge: How do we ensure every change is secure and compliant without slowing down development? Two terms frequently come up as solutions: IaC Security Scanning and Policy-as-Code (PaC).
While they both aim to secure your IaC, they are not the same. Understanding their differences is key to building a security strategy that is both effective and efficient. Think of it this way: IaC security scanning is like a spell checker finding known mistakes, while Policy-as-Code is the grammar rulebook that enforces your specific writing style. Let's break it down.
What is IaC Security Scanning? The Detective Control 🕵️
IaC security scanning tools are designed to detect known misconfigurations, vulnerabilities, and security anti-patterns in your code before it gets deployed. They act as a detective control, analyzing your Terraform, CloudFormation, Kubernetes manifests, or other configuration files against a pre-built library of security rules.
Primary Goal: To find and flag common security issues based on industry best practices (like CIS Benchmarks) and known vulnerabilities.
Checkov
An open-source static code analysis tool for IaC. It scans for misconfigurations in a wide range of file types, including Terraform, CloudFormation, and ARM templates. Best for broad framework support and a massive library of built-in policies.
tfsec
A static analysis tool focused specifically on Terraform. It's known for its speed and ability to trace issues back to the specific line of code that needs fixing. Best for fast, developer-friendly feedback within a Terraform-centric workflow.
Terrascan
A versatile IaC scanner that supports over 500 policies for various cloud providers and platforms, allowing for flexible integration into CI/CD pipelines. Best for organizations needing broad policy coverage.
When you run an IaC scanner in your CI/CD pipeline, it will fail the build if it finds, for example, an S3 bucket configured for public access or a security group with an inbound rule open to the world (0.0.0.0/0). It's an essential first line of defense.
What is Policy-as-Code (PaC)? The Preventive Guardrail 🏛️
Policy-as-Code takes a different approach. Instead of just looking for known bad practices, PaC allows you to define, manage, and enforce your own custom rules for what is considered acceptable in your environment. It acts as a preventive guardrail, ensuring that only compliant infrastructure can be provisioned.
Primary Goal: To enforce organization-specific governance, cost, operational, and security requirements that go beyond generic best practices.
How is this different?
An IaC scanner won't know your company's internal rules. For example, your rules might be:
- All AWS resources must be tagged with a
cost-centerandownertag. - EC2 instances cannot be larger than
t3.largein the development environment. - S3 buckets cannot be created outside of the
eu-west-1oreu-central-1regions. - Only the approved enterprise module for provisioning RDS can be used.
These aren't "security vulnerabilities" in the traditional sense, but they are critical governance policies for your organization. This is where PaC tools shine.
Open Policy Agent (OPA)
A general-purpose, open-source policy engine. Using its declarative language, Rego, you can write fine-grained policies for microservices, Kubernetes, CI/CD pipelines, and more. Best for unified, flexible policy enforcement across the entire cloud-native stack.
HashiCorp Sentinel
A policy-as-code framework embedded into HashiCorp's Enterprise products (like Terraform Cloud). It's designed to enforce policies on infrastructure changes before they are applied. Best for fine-grained governance directly within the Terraform Enterprise/Cloud ecosystem.
Head-to-Head: IaC Security vs. Policy-as-Code
Let's put them side-by-side to make the differences crystal clear.
| Feature | IaC Security Scanning | Policy-as-Code (PaC) |
|---|---|---|
| Primary Question | "Is this configuration a known vulnerability?" | "Does this configuration violate our rules?" |
| Control Type | Detective (Finds problems) | Preventive (Enforces rules) |
| Scope of Rules | Based on a public, pre-defined set of security best practices. | Custom-defined by the organization for security, cost, and operations. |
| Analogy | A virus scanner with a known signature database. | A firewall with a custom-configured ruleset. |
| Example Rule | Deny S3 buckets that allow public read access. | Deny S3 buckets that do not have versioning and object lock enabled. |
| Primary User | Developers, DevOps Engineers, Security Teams. | Platform Engineers, Security Architects, Compliance Teams. |
The Blurring Lines: A Note on Modern Tooling
While the core concepts of detecting known bad (IaC Scanning) and enforcing known good (PaC) are distinct, modern security tools have started to blend these capabilities.
💡 The Evolution of Security Platforms
Many platforms that started as IaC scanners now allow you to write custom rules, often using simplified languages or visual editors. Conversely, platforms built around PaC engines like OPA often come with pre-packaged policy libraries that check for common security misconfigurations (like CIS benchmarks).
The key difference today lies less in the tool's absolute features and more in its primary philosophy and architecture. Is it designed first and foremost to detect a wide array of public vulnerabilities, or is it architected to provide a flexible, universal engine for enforcing your organization's unique operational logic?
Better Together: A Layered Security Approach
The most effective security posture doesn't choose between IaC scanning and Policy-as-Code—it uses both. They address different aspects of risk and work together to create defense-in-depth.
Developer Commits Code
A developer pushes new Terraform code to a feature branch and opens a pull request.
Layer 1: IaC Security Scan
The CI pipeline triggers a fast scan (e.g., with tfsec) to catch common misconfigurations like public S3 buckets or open security groups. This provides immediate, basic feedback.
Layer 2: Policy-as-Code Check
If the first scan passes, the pipeline evaluates the Terraform plan against the organization's custom PaC policies (e.g., with OPA). Does the resource have correct tags? Is it in an approved region? Is it an allowed instance type?
Deployment
Only if both checks pass can the code be merged and deployed, ensuring it's free of known vulnerabilities AND compliant with internal governance.
This layered approach provides comprehensive coverage. The IaC scanner acts as a broad net for common errors, while PaC provides the fine-grained, context-aware enforcement needed for enterprise governance.