This is unreleased documentation for Policy Manager 1.23-next.

Quick start

The SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) stack comprises:

  • ClusterAdmissionPolicy resources: this is how policy definition happens for Kubernetes clusters.

  • PolicyServer resources: representing a deployment of a SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) PolicyServer. The Kubewarden PolicyServer loads and evaluates your administrator’s policies.

  • AdmissionPolicy resources: policies for a defined namespace.

  • A deployment of a kubewarden-controller: this controller monitors the ClusterAdmissionPolicy resources and interacts with the SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) PolicyServer components.

SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) describes its Kubernetes Custom Resource Definitions (CRDs) here.

SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) CRDs mentioned in this tutorial and in the rest of documentation have short names, which are easier to use. These are the short names for the CRDs:

Resource shortName

AdmissionPolicies

ap

ClusterAdmissionPolicies

cap

AdmissionPolicyGroups

apg

ClusterAdmissionPolicyGroups

capg

PolicyServers

ps

Installation

Authentication

You can retrieve SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) policies from the GitHub container registry at https://ghcr.io. You need authentication to use the repository with the SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) CLI, a GitHub personal access token (PAT). Their documentation guides you through creating one if you haven’t already done so. Then you authenticate with a command like:

echo $PAT | docker login ghcr.io --username <my-gh-username> --password-stdin

Deploy the SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) stack using helm charts as follows:

helm repo add kubewarden https://charts.kubewarden.io
helm repo update kubewarden

Install the following Helm charts in the kubewarden namespace in your Kubernetes cluster:

  • kubewarden-crds, which registers the ClusterAdmissionPolicy, AdmissionPolicy and PolicyServer Custom Resource Definitions. Also, the PolicyReport Custom Resource Definitions used by the audit scanner.

  • kubewarden-controller, which installs the SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) controller and the audit scanner

    If you need to disable the audit scanner component check the audit scanner installation documentation page.

  • kubewarden-defaults, which creates a PolicyServer resource named default. It can also install a set of recommended policies to secure your cluster by enforcing well known best practices.

helm install --wait -n kubewarden --create-namespace kubewarden-crds kubewarden/kubewarden-crds
helm install --wait -n kubewarden kubewarden-controller kubewarden/kubewarden-controller
helm install --wait -n kubewarden kubewarden-defaults kubewarden/kubewarden-defaults

Since v0.4.0, a PolicyServer resource named default isn’t created when using the kubewarden-controller chart. Now a Helm chart called kubewarden-defaults, installs the default policy server.

This means that if you aren’t using the latest version of the kubewarden-controller and are trying to upgrade or delete, your default policy server won’t be upgraded or deleted. So, you might run into issues if you try to install the kubewarden-defaults with certain conflicting information, for example, the same policy server name. To be able to use future upgrades in the kubewarden-defaults Helm chart remove the existing PolicyServer resource created by the kubewarden-controller before installing the new chart. Now you can update your policy server using Helm upgrades without resource conflicts. When you remove the PolicyServer, you remove all the policies bound to it too.

The default configuration values are sufficient for most deployments. The documentation describes all the options.

Main components

SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) has three main components which you interact with:

PolicyServer

The kubewarden-controller manages a SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) PolicyServer. You can deploy multiple {policy-servers}s in the same Kubernetes cluster.

A PolicyServer validates incoming requests by executing SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) policies against them.

This is the default PolicyServer configuration:

apiVersion: policies.kubewarden.io/v1
kind: PolicyServer
metadata:
  name: reserved-instance-for-tenant-a
spec:
  image: ghcr.io/kubewarden/policy-server:v1.3.0
  replicas: 2
  serviceAccountName: ~
  env:
    - name: KUBEWARDEN_LOG_LEVEL
      value: debug

Check the latest released PolicyServer version and change the tag to match.

Overview of the attributes of the PolicyServer resource:

Required Placeholder Description

Y

image

The name of the container image

Y

replicas

The number of desired instances

N

serviceAccountName

The name of the ServiceAccount to use for the PolicyServer deployment. If no value is provided, the default ServiceAccount from the namespace, where the kubewarden-controller is installed, will be used.

N

env

The list of environment variables

N

annotations

The list of annotations

Changing any of these attributes causes a PolicyServer deployment with the new configuration.

ClusterAdmissionPolicy

The ClusterAdmissionPolicy resource is the core of the SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) stack. It defines how policies evaluate requests.

Enforcing policies is the most common operation which a Kubernetes administrator performs. You can declare as many policies as you want, each targets one or more Kubernetes resources (that is, pods, Custom Resource and others). You also specify the type of operations applied to targeted resources. The operations available are CREATE, UPDATE, DELETE and CONNECT.

Default ClusterAdmissionPolicy configuration:

apiVersion: policies.kubewarden.io/v1
kind: ClusterAdmissionPolicy
metadata:
  name: psp-capabilities
spec:
  policyServer: reserved-instance-for-tenant-a
  module: registry://ghcr.io/kubewarden/policies/psp-capabilities:v0.1.9
  rules:
    - apiGroups: [""]
      apiVersions: ["v1"]
      resources: ["pods"]
      operations:
        - CREATE
        - UPDATE
  mutating: true
  settings:
    allowed_capabilities:
      - CHOWN
    required_drop_capabilities:
      - NET_ADMIN

Overview of the attributes of the ClusterAdmissionPolicy resource:

Required Placeholder Description

N

policy-server

Identifies an existing PolicyServer object. The policy will be served only by this PolicyServer instance. A ClusterAdmissionPolicy that doesn’t have an explicit PolicyServer, will be served by the one named default.

Y

module

The location of the SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) policy. The following schemes are allowed:

N

- registry: The policy is downloaded from an OCI artifacts compliant container registry. Example: registry://<OCI registry/policy URL>

N

- http, https: The policy is downloaded from a regular HTTP(s) server. Example: https://<website/policy URL>

N

- file: The policy is loaded from a file in the computer file system. Example: file:///<policy WASM binary full path>

Y

resources

The Kubernetes resources evaluated by the policy

Y

operations

What operations for the previously given types should be forwarded to this admission policy by the API server for evaluation.

Y

mutating

A boolean value that must be set to true for policies that can mutate incoming requests

N

settings

A free-form object that contains the policy configuration values

N

failurePolicy

The action to take if the request evaluated by a policy results in an error. The following options are allowed:

N

- Ignore: an error calling the webhook is ignored and the API request is allowed to continue

N

- Fail: an error calling the webhook causes the admission to fail and the API request to be rejected

The ClusterAdmissionPolicy resources are registered with a * webhook scope, which means that registered webhooks forward all requests matching the given resources and operations — either namespaced or cluster-wide resources.

AdmissionPolicy

AdmissionPolicy is a namespace-wide resource. The policy processes only the requests that are targeting the Namespace with the AdmissionPolicy defined. Other than that, there are no functional differences between the AdmissionPolicy and ClusterAdmissionPolicy resources.

AdmissionPolicy requires Kubernetes 1.21.0 or greater. This is because Kubewarden uses the kubernetes.io/metadata.name label, introduced in Kubernetes 1.21.0

The complete documentation of these Custom Resources can be found here or on docs.crds.dev.

Example: Enforce your first policy

We will use the pod-privileged policy. We want to prevent the creation of privileged containers inside our Kubernetes cluster by enforcing this policy.

Let’s define a ClusterAdmissionPolicy to do that:

kubectl apply -f - <<EOF
apiVersion: policies.kubewarden.io/v1
kind: ClusterAdmissionPolicy
metadata:
  name: privileged-pods
spec:
  module: registry://ghcr.io/kubewarden/policies/pod-privileged:v0.2.2
  rules:
  - apiGroups: [""]
    apiVersions: ["v1"]
    resources: ["pods"]
    operations:
    - CREATE
    - UPDATE
  mutating: false
EOF

This produces the following output:

clusteradmissionpolicy.policies.kubewarden.io/privileged-pods created

When defining a ClusterAdmissionPolicy, the status becomes pending, and it forces a rollout of the targeted PolicyServer. In our example, it’s the PolicyServer named default. You can monitor the rollout by running the following command:

kubectl get clusteradmissionpolicy.policies.kubewarden.io/privileged-pods

You should see the following output:

NAME              POLICY SERVER   MUTATING   STATUS
privileged-pods   default         false      pending

Once the new policy is ready to be served, the kubewarden-controller registers a ValidatingWebhookConfiguration object.

The ClusterAdmissionPolicy status becomes active once the Deployment is done for every PolicyServer instance. Show ValidatingWebhookConfigurations with the following command:

kubectl get validatingwebhookconfigurations.admissionregistration.k8s.io -l kubewarden

You should see the following output:

NAME                          WEBHOOKS   AGE
clusterwide-privileged-pods   1          9s

Once the ClusterAdmissionPolicy is active and the ValidatingWebhookConfiguration registers, you can test the policy.

First, you can create a Pod with a Container not in privileged mode:

kubectl apply -f - <<EOF
apiVersion: v1
kind: Pod
metadata:
  name: unprivileged-pod
spec:
  containers:
    - name: nginx
      image: nginx:latest
EOF

This produces the following output:

pod/unprivileged-pod created

The Pod is successfully created.

Now, you can create a Pod with at least one Container privileged flag:

kubectl apply -f - <<EOF
apiVersion: v1
kind: Pod
metadata:
  name: privileged-pod
spec:
  containers:
    - name: nginx
      image: nginx:latest
      securityContext:
          privileged: true
EOF

The policy denies creation of the Pod and you should see the following message:

Error from server: error when creating "STDIN": admission webhook "clusterwide-privileged-pods.kubewarden.admission" denied the request: Privileged container is not allowed

Both examples didn’t define a namespace, which means the default namespace was the target. However, as you could see in the second example, the policy is still applied. As stated previously, this is due to the scope being cluster-wide and not targeting a specific namespace.

Uninstall

You can remove the resources created by uninstalling the helm charts as follows:

helm uninstall --namespace kubewarden kubewarden-defaults
helm uninstall --namespace kubewarden kubewarden-controller
helm uninstall --namespace kubewarden kubewarden-crds

After removal of the helm charts remove the Kubernetes namespace used to deploy the SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) stack:

kubectl delete namespace kubewarden

SUSE® Rancher Prime: Admission Policy Manager (Kubewarden) contains a helm pre-delete hook that removes all PolicyServer`s and `kubewarden-controller`s. Then the `kubewarden-controller deletes all resources, so it’s important that kubewarden-controller is running when helm uninstall executes.

Kubewarden deletes ValidatingWebhookConfigurations and MutatingWebhookConfigurations. Check this with:

kubectl get validatingwebhookconfigurations.admissionregistration.k8s.io -l "kubewarden"
kubectl get mutatingwebhookconfigurations.admissionregistration.k8s.io -l "kubewarden"

If these resources aren’t automatically removed, remove them manually using the following command:

kubectl delete -l "kubewarden" validatingwebhookconfigurations.admissionregistration.k8s.io
kubectl delete -l "kubewarden" mutatingwebhookconfigurations.admissionregistration.k8s.io

Wrapping up

ClusterAdmissionPolicy is the core resource that a cluster operator has to manage. The kubewarden-controller module automatically takes care of the configuration for the rest of the resources needed to run the policies.

What’s next?

Now, you are ready to deploy SUSE® Rancher Prime: Admission Policy Manager (Kubewarden)! Have a look at the policies on artifacthub.io, on GitHub, or reuse existing Rego policies as shown in the following chapters.

Full list of available policies on ArtifactHub