implementing-policy-as-code-with-open-policy-agent

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---
name: implementing-policy-as-code-with-open-policy-agent
description: 'Implements policy-as-code enforcement with Open Policy Agent (OPA)
  and Gatekeeper for Kubernetes and CI/CD pipelines, covering writing Rego policies,
  deploying OPA Gatekeeper as a Kubernetes admission controller, testing policies
  in development, and integrating policy evaluation into deployment pipelines. Use
  when writing Rego policies, deploying Gatekeeper admission control, or gating
  CI/CD pipelines with policy-as-code checks.

  '
domain: cybersecurity
subdomain: devsecops
tags:
- devsecops
- cicd
- opa
- gatekeeper
- policy-as-code
- kubernetes
- secure-sdlc
version: 1.0.0
author: mahipal
license: Apache-2.0
nist_ai_rmf:
- GOVERN-1.1
- MEASURE-2.7
- MANAGE-3.1
nist_csf:
- PR.PS-01
- GV.SC-07
- ID.IM-04
- PR.PS-04
mitre_attack:
- T1195
- T1554
- T1059.004
- T1610
- T1611
---

# Implementing Policy as Code with Open Policy Agent

## When to Use

- When enforcing organizational security policies across Kubernetes clusters programmatically
- When requiring admission control that blocks non-compliant resources from being created
- When implementing policy governance that can be version-controlled, tested, and audited
- When standardizing security rules across multiple clusters and environments
- When needing a flexible policy engine that extends beyond Kubernetes to APIs and CI/CD

**Do not use** for vulnerability scanning (use Trivy/Checkov), for runtime threat detection (use Falco), or for network policy enforcement (use Kubernetes NetworkPolicy or Calico).

## Prerequisites

- Kubernetes cluster with admin access for Gatekeeper installation
- Helm for Gatekeeper deployment
- OPA CLI or conftest for local policy testing
- Rego knowledge for policy authoring

## Workflow

### Step 1: Install OPA Gatekeeper

```bash
# Install Gatekeeper via Helm
helm repo add gatekeeper https://open-policy-agent.github.io/gatekeeper/charts
helm install gatekeeper gatekeeper/gatekeeper \
  --namespace gatekeeper-system --create-namespace \
  --set replicas=3 \
  --set audit.replicas=1 \
  --set audit.writeToRAMDisk=true
```

### Step 2: Create Constraint Templates

```yaml
# templates/k8s-required-labels.yaml
apiVersion: templates.gatekeeper.sh/v1
kind: ConstraintTemplate
metadata:
  name: k8srequiredlabels
spec:
  crd:
    spec:
      names:
        kind: K8sRequiredLabels
      validation:
        openAPIV3Schema:
          type: object
          properties:
            labels:
              type: array
              items:
                type: string
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package k8srequiredlabels
        violation[{"msg": msg}] {
          provided := {label | input.review.object.metadata.labels[label]}
          required := {label | label := input.parameters.labels[_]}
          missing := required - provided
          count(missing) > 0
          msg := sprintf("Missing required labels: %v", [missing])
        }

---
# templates/k8s-container-limits.yaml
apiVersion: templates.gatekeeper.sh/v1
kind: ConstraintTemplate
metadata:
  name: k8scontainerlimits
spec:
  crd:
    spec:
      names:
        kind: K8sContainerLimits
      validation:
        openAPIV3Schema:
          type: object
          properties:
            cpu:
              type: string
            memory:
              type: string
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package k8scontainerlimits
        violation[{"msg": msg}] {
          container := input.review.object.spec.containers[_]
          not container.resources.limits.cpu
          msg := sprintf("Container %v has no CPU limit", [container.name])
        }
        violation[{"msg": msg}] {
          container := input.review.object.spec.containers[_]
          not container.resources.limits.memory
          msg := sprintf("Container %v has no memory limit", [container.name])
        }

---
# templates/k8s-block-privileged.yaml
apiVersion: t