Quick start

The Kubewarden stack comprises:

• Some ClusterAdmissionPolicy resources: this is how policies are defined for Kubernetes clusters

• Some PolicyServer resources: representing a deployment of a Kubewarden PolicyServer. Your administrator's policies are loaded and evaluated by the Kubewarden PolicyServer

• Some AdmissionPolicy resources: policies for a defined namespace

• A deployment of a kubewarden-controller: this controller monitors the ClusterAdmissionPolicy resources and interacts with the Kubewarden PolicyServer components.

tip

The Kubernetes Custom Resource Definitions (CRD) defined by Kubewarden are described here.

Installation

Prerequisites

The Helm chart depends on cert-manager. Ensure you install cert-manager before the kubewarden-controller chart.

You install the latest version of cert-manager by running the following commands:

kubectl apply -f https://github.com/jetstack/cert-manager/releases/latest/download/cert-manager.yaml

kubectl wait --for=condition=Available deployment --timeout=2m -n cert-manager --all

Authentication

Kubewarden policies can be retrieved from the GitHub container registry at https://ghcr.io. You need authentication to use the repository with the Kubewarden CLI, a GitHub personal access token (PAT). Their documentation guides you through creating one if you have not already done so. Then you authenticate with a command like:

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

Deploy the Kubewarden stack using helm charts as follows:

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

helm repo update kubewarden

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

• kubewarden-crds, which will register the ClusterAdmissionPolicy, AdmissionPolicy and PolicyServer Custom Resource Definitions. As well as the PolicyReport Custom Resource Definitions used by the audit scanner

• kubewarden-controller, which will install the Kubewarden controller and the audit scanner

note

If you want to disable the audit scanner component. Please check out the audit scanner installation docs page.

• kubewarden-defaults, which will create a PolicyServer resource named default. It can also install a set of recommended policies to secure your cluster by enforcing some 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

caution

Since v0.4.0, a PolicyServer resource named default will not be created using the kubewarden-controller chart. Now a Helm chart called kubewarden-defaults, installs the default policy server.

This means that if you are not using the latest version of the kubewarden-controller and are trying to upgrade or delete, your default policy server will not be upgraded or deleted. So, you might run into issues if you try to install the kubewarden-defaults with some conflicting information, for example, the same policy server name. To be able to take advantage of 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, all the policies bound to it will be removed as well.

The default configuration values are sufficient for most deployments. All options are documented here.

Main components

Kubewarden has three main components which you will interact with:

• The PolicyServer
• The ClusterAdmissionPolicy
• The AdmissionPolicy

PolicyServer

A Kubewarden PolicyServer is managed by the kubewarden-controller and multiple PolicyServers can be deployed in the same Kubernetes cluster.

A PolicyServer validates incoming requests by executing 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

note

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 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 will target one or more Kubernetes resources (i.e., pods, Custom Resource). You will also specify the type of operations to be 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 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

note

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

AdmissionPolicy

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

info

AdmissionPolicy requires Kubernetes 1.21.0 or above. This is because we are using the kubernetes.io/metadata.name label, which was 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 a ClusterAdmissionPolicy is defined, the status is set to pending, and it will force 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 will register a ValidatingWebhookConfiguration object.

The ClusterAdmissionPolicy status will be set to active once the Deployment is done for every PolicyServer instance. Show ValidatingWebhookConfiguration 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 is registered, you can test the policy.

First, let's 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 will produce the following output:

pod/unprivileged-pod created

The Pod is successfully created.

Now, let's 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 creation of the Pod has been denied by the policy 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

note

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 above, 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

Once the helm charts have been uninstalled, remove the Kubernetes namespace that was used to deploy the Kubewarden stack:

kubectl delete namespace kubewarden

caution

Kubewarden contains a helm pre-delete hook that will remove all PolicyServers and kubewarden-controller. Then the kubewarden-controller will delete all resources, so it is important that kubewarden-controller is running when helm uninstall is executed.

ValidatingWebhookConfigurations and MutatingWebhookConfigurations created by kubewarden should be deleted, this can be checked with:

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

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

If these resources are not automatically removed, remove them manually by 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.

Now, you are ready to deploy Kubewarden! Have a look at the policies on hub.kubewarden.io, on GitHub, or reuse existing Rego policies as shown in the following chapters.