Kyverno Has a Free API: Kubernetes-Native Policy Engine Without Learning Rego

Kyverno is a policy engine designed for Kubernetes. It lets you validate, mutate, and generate Kubernetes resources using simple YAML policies — no need to learn Rego or any new language.

What Is Kyverno?

Kyverno is a CNCF incubating project that manages policies as Kubernetes resources. Unlike OPA/Gatekeeper which requires learning Rego, Kyverno policies are written in familiar YAML with pattern matching.

Key Features:

• Policies as Kubernetes resources (YAML)
• No new language to learn
• Validate, mutate, and generate resources
• Image verification and signing
• Policy reports and audit mode
• CLI for testing policies
• Background scanning
• Exception management

Installation

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

# Install CLI
brew install kyverno

Validation Policies

# Require resource limits on all containers
apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: require-resource-limits
spec:
  validationFailureAction: Enforce
  rules:
    - name: check-limits
      match:
        any:
          - resources:
              kinds:
                - Pod
      validate:
        message: "All containers must have CPU and memory limits."
        pattern:
          spec:
            containers:
              - resources:
                  limits:
                    memory: "?*"
                    cpu: "?*"
---
# Disallow latest tag
apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: disallow-latest-tag
spec:
  validationFailureAction: Enforce
  rules:
    - name: no-latest
      match:
        any:
          - resources:
              kinds:
                - Pod
      validate:
        message: "Using ':latest' tag is not allowed."
        pattern:
          spec:
            containers:
              - image: "!*:latest"

Mutation Policies

# Auto-add labels to all pods
apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: add-default-labels
spec:
  rules:
    - name: add-team-label
      match:
        any:
          - resources:
              kinds:
                - Pod
      mutate:
        patchStrategicMerge:
          metadata:
            labels:
              managed-by: kyverno
              environment: "{{request.namespace}}"
---
# Auto-add resource defaults
apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: default-resources
spec:
  rules:
    - name: set-defaults
      match:
        any:
          - resources:
              kinds:
                - Pod
      mutate:
        patchStrategicMerge:
          spec:
            containers:
              - (name): "*"
                resources:
                  requests:
                    memory: "64Mi"
                    cpu: "50m"
                  limits:
                    memory: "256Mi"
                    cpu: "200m"

Generation Policies

# Auto-create NetworkPolicy for every new namespace
apiVersion: kyverno.io/v1
kind: ClusterPolicy
metadata:
  name: generate-default-netpol
spec:
  rules:
    - name: default-deny
      match:
        any:
          - resources:
              kinds:
                - Namespace
      generate:
        kind: NetworkPolicy
        apiVersion: networking.k8s.io/v1
        name: default-deny-ingress
        namespace: "{{request.object.metadata.name}}"
        data:
          spec:
            podSelector: {}
            policyTypes:
              - Ingress

Kyverno API: Programmatic Policy Management

from kubernetes import client, config

config.load_kube_config()
custom = client.CustomObjectsApi()

# List all policies
policies = custom.list_cluster_custom_object(
    group="kyverno.io",
    version="v1",
    plural="clusterpolicies"
)
for policy in policies["items"]:
    rules = policy["spec"].get("rules", [])
    action = policy["spec"].get("validationFailureAction", "Audit")
    print(f"Policy: {policy['metadata']['name']}, Rules: {len(rules)}, Action: {action}")

# Get policy reports
reports = custom.list_namespaced_custom_object(
    group="wgpolicyk8s.io",
    version="v1alpha2",
    namespace="default",
    plural="policyreports"
)
for report in reports["items"]:
    results = report.get("results", [])
    passed = sum(1 for r in results if r["result"] == "pass")
    failed = sum(1 for r in results if r["result"] == "fail")
    print(f"Report: {report['metadata']['name']}, Passed: {passed}, Failed: {failed}")

CLI Testing

# Test policy against a resource
kyverno apply policy.yaml -r deployment.yaml

# Test all policies in a directory
kyverno apply ./policies/ -r ./resources/

# Validate policy syntax
kyverno validate ./policies/

Resources

• Kyverno Docs
• Kyverno GitHub — 5.5K+ stars
• Policy Library

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