Policy-as-Code: Shifting Left to Secure Cloud Infrastructure



In this article, we discuss the concept of policy-as-code, its integration with Continuous Deployment (CD) pipelines, and the benefits of shifting left. Policy-as-code is a security approach that involves writing policies in a declarative format, such as JSON or YAML, and then using those policies to automate the enforcement of security controls. This can be done by integrating policy-as-code tools with CD pipelines, which are used to automate the deployment of changes to production systems. By shifting security left, or incorporating security into the development process earlier, organizations can reduce the risk of security vulnerabilities being introduced into production systems.

We will explore how Policy-as-Code gates in the CICD pipeline can enhance cloud infrastructure security. A policy-as-code gate is a mechanism that allows organizations to enforce security policies as part of the CICD process. This can be done by using a policy-as-code tool to validate that the proposed changes to the cloud infrastructure comply with the organization's security policies. If the changes do not comply with the policies, the CD process will be blocked until the changes are made to comply with the policies.

We'll delve into the use of HashiCorp Sentinel to enforce policy compliance, with Terraform code examples to illustrate the process. HashiCorp Sentinel is a policy-as-code tool that can be used to enforce security policies in cloud infrastructure. Terraform is a tool that can be used to manage infrastructure as code. We will use Terraform to create a cloud infrastructure and then use Sentinel to enforce security policies on that infrastructure.

Policy-as-Code: A Paradigm Shift for Infrastructure Security

The Emergence of Policy-as-Code

Policy-as-Code is an emerging approach to managing infrastructure security and compliance in the cloud. It entails the automation of policy enforcement through codified policies, which are integrated into the development and deployment processes. This technique has become increasingly popular as organizations recognize the need for enhanced security measures in their cloud environments.

The Role of Policy-as-Code in Continuous Deployment Pipelines

In a Continuous Deployment pipeline, Policy-as-Code is employed to introduce security gates that validate infrastructure changes before they are applied. These gates allow organizations to maintain the desired security posture, even as new infrastructure components are added or existing ones are modified. By integrating Policy-as-Code into the CD pipeline, security and compliance requirements can be evaluated at every stage of the development and deployment process.

HashiCorp Sentinel: A Powerful Policy-as-Code Framework

An Introduction to HashiCorp Sentinel

Sentinel is an extensible policy-as-code framework developed by HashiCorp. It is designed to enforce fine-grained, logic-based policies across the entire HashiCorp product suite, including Terraform Cloud. Sentinel policies are written in a high-level, declarative language that is both easy to read and write. They are evaluated during Terraform runs, enabling organizations to ensure that infrastructure changes adhere to established security and compliance requirements.

Sentinel Policy Evaluation in Terraform Cloud

In Terraform Cloud, Sentinel policies are integrated into workspaces to enforce policy compliance as part of the Terraform run process. When a Terraform run is initiated, Sentinel policies are evaluated against the proposed infrastructure changes. If any policy violations are detected, the run is marked as failed, and the violations are reported. This mechanism prevents organizations from applying non-compliant changes to their cloud infrastructure.

Enforcing Policy Compliance with Terraform and Sentinel

Creating a Publicly Accessible S3 Bucket with Terraform

Consider the following Terraform code snippet, which creates an AWS S3 bucket with public read access:\

resource "aws_s3_bucket" "example" {
bucket = "my-public-bucket" 
 acl = "public-read" 
 policy = jsonencode({
 Version = "2012-10-17"
 Statement = [     
  Action = "s3:GetObject"       
   Effect = "Allow"       
   Resource = "arn:aws:s3:::my-public-bucket/*"       
   Principal = "*"     

This code defines an S3 bucket with the "public-read" access control list (ACL) and an associated policy that allows anyone to read objects within the bucket.

Detecting Publicly Accessible S3 Buckets with a Sentinel Policy

Now, let's assume that our organization has a policy prohibiting the creation of publicly accessible S3 buckets. We can enforce this policy using Sentinel by writing the following policy:

import "tfplan/v2" as tfplan
main = rule {
all tfplan.resource_changes as _, resource_changes{
resource_changes.mode is "managed" and
resource_changes.type is "aws_s3_bucket" and
resource_changes.change.actions contains "create" implies not is_public_acl(resource_changes.change.after)
is_public_acl = func(bucket) {
bucket.acl is "public-read" or bucket.acl is "public-read-write"}

This Sentinel policy imports the `tfplan/v2` module to evaluate the Terraform plan for any changes to S3 bucket resources. It checks for the creation of new S3 buckets and uses the `is_public_acl` function to determine if the bucket has a public ACL. If a publicly accessible bucket is found, the policy evaluation fails, preventing the Terraform run from proceeding.

The Benefits of Shifting Left with Policy-as-Code

Improved Security Posture

By incorporating Policy-as-Code gates into the CD pipeline, organizations can enforce security and compliance requirements at every infrastructure development and deployment stage. This proactive approach helps maintain a strong security posture, even as cloud environments evolve and grow in complexity.

Early Detection of Compliance Issues

Shifting left with policy-as-code allows organizations to identify and address compliance issues early in development, reducing the risk of costly and time-consuming remediation efforts later. This approach also minimizes the likelihood of introducing security vulnerabilities into production environments, further bolstering overall security.

Streamlined Collaboration and Consistency

Integrating policy-as-code into the CD pipeline fosters collaboration between security, development, and operations teams by establishing a shared understanding of security and compliance requirements. This approach promotes consistency in infrastructure security, making it easier for organizations to achieve and maintain compliance with industry standards and regulations.

Enhanced Auditability and Traceability

Policy-as-Code provides a clear, auditable record of security and compliance requirements and their enforcement throughout the infrastructure lifecycle. This transparency enables organizations to demonstrate their commitment to security and compliance, which can be particularly valuable during audits, assessments, and certifications.

In summary, implementing Policy-as-Code and shifting left in the CD pipeline empowers organizations to secure their cloud infrastructure effectively and proactively. Using tools like HashiCorp Sentinel and Terraform can enforce robust, logic-based policies that ensure compliance with organizational and regulatory requirements. The benefits of this approach include improved security posture, early detection of compliance issues, streamlined collaboration, and enhanced audibility, all of which contribute to the overall security and stability of an organization's cloud environment.

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