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Kubernetes Policy Management

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By Muzammil Shaik 9 min read

🛡️ Kubernetes Policy Management

As Kubernetes adoption grows within organizations, ensuring consistent security, compliance, and operational standards becomes increasingly challenging. Kubernetes Policy Management addresses this challenge by providing a framework for defining, enforcing, and auditing policies across your Kubernetes clusters.

🌟 What is Kubernetes Policy Management?

Kubernetes Policy Management refers to the practice of defining and enforcing rules that govern how resources are created, configured, and operated within a Kubernetes cluster. These policies can cover a wide range of concerns:

  • Security: Ensuring workloads follow security best practices
  • Compliance: Meeting regulatory requirements
  • Operational Excellence: Enforcing organizational standards
  • Cost Optimization: Preventing resource waste
  • Reliability: Ensuring high availability and fault tolerance

🔑 Why Policy Management Matters

  1. Preventative Security: Stop security issues before they happen
  2. Consistent Compliance: Ensure all workloads meet regulatory requirements
  3. Reduced Human Error: Automate policy enforcement to prevent mistakes
  4. Scalable Governance: Apply consistent standards across multiple clusters
  5. Auditability: Track policy violations and compliance status

🛠️ Policy Management Tools

🔍 Open Policy Agent (OPA) Gatekeeper

OPA Gatekeeper is a CNCF project that provides policy-based control for cloud-native environments, with specific integration for Kubernetes.

Key Features of OPA Gatekeeper

  • Admission Control: Validate and mutate resources at creation time
  • Audit: Check existing resources against policies
  • Constraint Templates: Reusable policy definitions
  • Rego Language: Powerful policy language for complex rules
  • Library: Growing collection of community-contributed policies

Installing OPA Gatekeeper

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# Install Gatekeeper using Helm
helm repo add gatekeeper https://open-policy-agent.github.io/gatekeeper/charts
helm install gatekeeper gatekeeper/gatekeeper --namespace gatekeeper-system --create-namespace

Gatekeeper Constraint Templates

Constraint Templates define the schema and logic for policies:

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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, "details": {"missing_labels": missing}}] {
          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])
        }

Gatekeeper Constraints

Constraints are instances of Constraint Templates that define specific rules:

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apiVersion: constraints.gatekeeper.sh/v1beta1
kind: K8sRequiredLabels
metadata:
  name: require-team-label
spec:
  match:
    kinds:
      - apiGroups: [""]
        kinds: ["Namespace"]
  parameters:
    labels: ["team"]

Common Gatekeeper Policies

Require Resource Limits

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apiVersion: templates.gatekeeper.sh/v1
kind: ConstraintTemplate
metadata:
  name: k8srequiredresources
spec:
  crd:
    spec:
      names:
        kind: K8sRequiredResources
      validation:
        openAPIV3Schema:
          type: object
          properties:
            limits:
              type: array
              items:
                type: string
            requests:
              type: array
              items:
                type: string
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package k8srequiredresources

        violation[{"msg": msg}] {
          container := input.review.object.spec.containers[_]
          required_limit := input.parameters.limits[_]
          not container.resources.limits[required_limit]
          msg := sprintf(
            "Container %v is missing required limit %v",
            [container.name, required_limit]
          )
        }

        violation[{"msg": msg}] {
          container := input.review.object.spec.containers[_]
          required_request := input.parameters.requests[_]
          not container.resources.requests[required_request]
          msg := sprintf(
            "Container %v is missing required request %v",
            [container.name, required_request]
          )
        }
---
apiVersion: constraints.gatekeeper.sh/v1beta1
kind: K8sRequiredResources
metadata:
  name: container-must-have-limits-and-requests
spec:
  match:
    kinds:
      - apiGroups: [""]
        kinds: ["Pod"]
  parameters:
    limits: ["cpu", "memory"]
    requests: ["cpu", "memory"]

Restrict Repository Sources

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apiVersion: templates.gatekeeper.sh/v1
kind: ConstraintTemplate
metadata:
  name: k8sallowedrepos
spec:
  crd:
    spec:
      names:
        kind: K8sAllowedRepos
      validation:
        openAPIV3Schema:
          type: object
          properties:
            repos:
              type: array
              items:
                type: string
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package k8sallowedrepos

        violation[{"msg": msg}] {
          container := input.review.object.spec.containers[_]
          image := container.image
          repo := split_image(image)[0]
          not repo_is_allowed(repo)
          msg := sprintf(
            "Container %v uses disallowed image repo %v, allowed repos are %v",
            [container.name, repo, input.parameters.repos]
          )
        }

        split_image(image) = [repo, tag] {
          parts := split(image, ":")
          count(parts) == 2
          repo := parts[0]
          tag := parts[1]
        }

        split_image(image) = [image, "latest"] {
          not contains(image, ":")
        }

        repo_is_allowed(repo) {
          allowed_repo := input.parameters.repos[_]
          startswith(repo, allowed_repo)
        }
---
apiVersion: constraints.gatekeeper.sh/v1beta1
kind: K8sAllowedRepos
metadata:
  name: only-approved-image-repos
spec:
  match:
    kinds:
      - apiGroups: [""]
        kinds: ["Pod"]
  parameters:
    repos:
      - "docker.io/company/"
      - "gcr.io/company/"

📋 Kyverno

Kyverno is a policy engine designed specifically for Kubernetes, with a focus on simplicity and ease of use.

Key Features of Kyverno

  • YAML-based Policies: No need to learn a new language
  • Validation, Mutation, Generation: Complete policy lifecycle
  • Image Verification: Validate image signatures and attestations
  • CLI and Reporting: Tools for testing and reporting
  • Policy Exceptions: Flexible policy exceptions

Installing Kyverno

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# Install Kyverno using Helm
helm repo add kyverno https://kyverno.github.io/kyverno/
helm install kyverno kyverno/kyverno --namespace kyverno --create-namespace

Kyverno Policy Structure

Kyverno policies are defined using the ClusterPolicy or Policy resource:

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apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: require-labels
spec:
  validationFailureAction: enforce
  background: true
  rules:
  - name: require-team-label
    match:
      resources:
        kinds:
        - Namespace
    validate:
      message: "The label 'team' is required."
      pattern:
        metadata:
          labels:
            team: "?*"

Common Kyverno Policies

Require Resource Limits

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apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: require-resource-limits
spec:
  validationFailureAction: enforce
  background: true
  rules:
  - name: validate-resources
    match:
      resources:
        kinds:
        - Pod
    validate:
      message: "CPU and memory resource limits are required"
      pattern:
        spec:
          containers:
          - resources:
              limits:
                memory: "?*"
                cpu: "?*"
              requests:
                memory: "?*"
                cpu: "?*"

Restrict Repository Sources

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apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: restrict-image-registries
spec:
  validationFailureAction: enforce
  background: true
  rules:
  - name: validate-registries
    match:
      resources:
        kinds:
        - Pod
    validate:
      message: "Only images from approved registries are allowed"
      pattern:
        spec:
          containers:
          - image: "docker.io/company/*" | "gcr.io/company/*"

Generate Network Policy

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apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: add-networkpolicy
spec:
  background: false
  rules:
  - name: default-deny-ingress
    match:
      resources:
        kinds:
        - Namespace
    exclude:
      resources:
        namespaces:
        - kube-system
        - kube-public
        - default
    generate:
      kind: NetworkPolicy
      name: default-deny-ingress
      namespace: ""
      data:
        spec:
          podSelector: {}
          policyTypes:
          - Ingress

🔄 Comparing OPA Gatekeeper and Kyverno

Feature OPA Gatekeeper Kyverno
Policy Language Rego (custom language) YAML (native Kubernetes)
Learning Curve Steeper (requires learning Rego) Gentler (uses familiar YAML)
Flexibility Very flexible with complex rules Good for common use cases
Performance Good performance Good performance
Mutation Supported (beta) Fully supported
Generation Not supported Fully supported
Image Verification Not built-in Built-in
CLI Tools Limited Comprehensive
Community CNCF Incubating CNCF Incubating
Adoption Widely adopted Growing adoption

🌟 Best Practices for Policy Management

  1. Start with Audit Mode
    • Begin with non-enforcing policies to understand impact
    • Gradually move to enforcement as confidence grows
    • Use validationFailureAction: audit in Kyverno or enforcementAction: dryrun in Gatekeeper
  2. Layer Policies
    • Implement basic policies first (resource requirements, labels)
    • Add more complex policies as maturity increases
    • Group policies by concern (security, compliance, operations)
  3. Document Policies
    • Clearly document the purpose of each policy
    • Explain how to comply with policies
    • Provide contact information for policy exceptions
  4. Implement Exception Mechanisms
    • Define a process for policy exceptions
    • Use namespaces or labels to exclude certain workloads
    • Document all exceptions with justification and expiration
  5. Test Policies
    • Test policies in development environments
    • Use CLI tools to validate policies before applying
    • Implement CI/CD for policy testing
  6. Monitor and Report
    • Monitor policy violations
    • Generate regular compliance reports
    • Track policy effectiveness over time

🚀 Common Policy Categories

1. Security Policies

  • Privileged Containers: Prevent privileged containers
  • Host Path Mounts: Restrict access to host paths
  • Capabilities: Limit container capabilities
  • User and Group IDs: Enforce non-root users
  • Seccomp and AppArmor: Require security profiles

2. Compliance Policies

  • Required Labels: Enforce labeling standards
  • Resource Quotas: Enforce resource limits
  • Network Policies: Ensure network segmentation
  • Sensitive Data: Prevent secrets in environment variables
  • Image Sources: Restrict to approved registries

3. Operational Policies

  • Health Checks: Require liveness and readiness probes
  • Pod Disruption Budgets: Ensure high availability
  • Anti-Affinity: Enforce distribution across nodes
  • Resource Requests: Ensure proper scheduling
  • Annotations: Enforce required annotations

🏁 Implementing a Policy Management Strategy

  1. Assess Your Needs
    • Identify regulatory requirements
    • Document organizational standards
    • Prioritize security concerns
  2. Choose a Tool
    • Select OPA Gatekeeper for complex rules and flexibility
    • Choose Kyverno for simplicity and ease of use
    • Consider using both for different use cases
  3. Develop a Policy Roadmap
    • Start with critical security policies
    • Add compliance policies
    • Implement operational best practices
  4. Implement Gradually
    • Begin with audit mode
    • Communicate with stakeholders
    • Provide documentation and training
  5. Monitor and Improve
    • Track policy violations
    • Gather feedback from users
    • Continuously refine policies

🌟 Example Policy Implementation Plan

Phase 1: Foundation (Audit Mode)

  1. Required labels for resources
  2. Resource limits and requests
  3. Restricted repositories
  4. Non-privileged containers

Phase 2: Security (Enforcement)

  1. Enforce resource limits
  2. Prevent privileged containers
  3. Restrict host mounts
  4. Enforce network policies

Phase 3: Compliance

  1. PCI-DSS specific controls
  2. HIPAA requirements
  3. SOC 2 controls
  4. Industry-specific regulations

Phase 4: Operational Excellence

  1. Health check requirements
  2. High availability controls
  3. Disaster recovery policies
  4. Cost optimization rules

📚 Additional Resources

🏁 Conclusion

Kubernetes Policy Management is essential for organizations looking to scale their Kubernetes deployments while maintaining security, compliance, and operational standards. By implementing policy-as-code using tools like OPA Gatekeeper or Kyverno, organizations can automate policy enforcement, reduce human error, and ensure consistent standards across their Kubernetes environments.

Whether you choose OPA Gatekeeper for its flexibility and powerful Rego language or Kyverno for its simplicity and native YAML approach, the key is to implement a comprehensive policy management strategy that addresses your organization’s specific needs and gradually moves from audit to enforcement as your confidence and maturity grow.

Remember that policy management is not a one-time effort but an ongoing process of refinement and improvement as your Kubernetes environment evolves and new requirements emerge.

Devops
Kubernetes DevOps Security Compliance Policy Management OPA Gatekeeper Kyverno
This post is licensed under CC BY 4.0 by the author.