Kyverno is a policy engine designed for Kubernetes. Here are some of its features:
- policies as Kubernetes resources (no new language to learn!)
- validate, mutate, or generate any resource
- match resources using label selectors and wildcards
- validate and mutate using overlays (like Kustomize!)
- synchronize configurations across namespaces
- block non-conformant resources using admission controls, or report policy violations
- test policies and validate resources using the Kyverno CLI, in your CI/CD pipeline, before applying to your cluster
policies-as-codeusing familiar tools like Git and Kustomize
Kyverno allows cluster administrators to manage environment specific configurations independently of workload configurations and enforce configuration best practices for their clusters. Kyverno can be used to scan existing workloads for best practices, or can be used to enforce best practices by blocking or mutating API requests.
How Kyverno works
Kyverno runs as a dynamic admission controller in a Kubernetes cluster. Kyverno receives validating and mutating admission webhook HTTP callbacks from the kube-apiserver and applies matching policies to return results that enforce admission policies or reject requests.
Kyverno policies can match resources using the resource kind, name, and label selectors. Wildcards are supported in names.
Mutating policies can be written as overlays (similar to Kustomize) or as a RFC 6902 JSON Patch. Validating policies also use an overlay style syntax, with support for pattern matching and conditional (if-then-else) processing.
Policy enforcement is captured using Kubernetes events. Kyverno also reports policy violations for existing resources.
This section will help you install Kyverno and create your first policy:
NoteYour Kubernetes cluster version must be above v1.14 which adds webhook timeouts. To check the version, enter
kubectl create -f https://raw.githubusercontent.com/kyverno/kyverno/main/definitions/release/install.yaml
You can also install Kyverno using a Helm chart:
# Add the Helm repository helm repo add kyverno https://kyverno.github.io/kyverno/ # Create a namespace kubectl create ns kyverno # Install the kyverno helm chart helm install kyverno --namespace kyverno kyverno/kyverno
Add the policy below to your cluster. It contains a single validation rule that requires that all pods have a
app.kubernetes.io/name label. Kyverno supports different rule types to validate, mutate, and generate configurations. The policy attribute
validationFailureAction is set to
enforce to block API requests that are non-compliant (using the default value
audit will report violations but not block requests.)
apiVersion: kyverno.io/v1 kind: ClusterPolicy metadata: name: require-labels spec: validationFailureAction: enforce rules: - name: check-for-labels match: resources: kinds: - Pod validate: message: "label `app.kubernetes.io/name` is required" pattern: metadata: labels: app.kubernetes.io/name: "?*"
Try creating a deployment without the required label:
kubectl create deployment nginx --image=nginx
You should see an error:
Error from server: admission webhook "nirmata.kyverno.resource.validating-webhook" denied the request: resource Deployment/default/nginx was blocked due to the following policies require-labels: autogen-check-for-labels: 'Validation error: label `app.kubernetes.io/name` is required; Validation rule autogen-check-for-labels failed at path /spec/template/metadata/labels/app.kubernetes.io/name/'
Create a pod with the required label. For example, using this command:
kubectl run nginx --image nginx --labels app.kubernetes.io/name=nginx
This pod configuration is compliant with the policy rules, and is not blocked.
Clean up by deleting all cluster policies:
kubectl delete cpol --all