Version: v1.6

Working with Gatekeeper(OPA)

Gatekeeper , is a customizable admission webhook for Kubernetes that enforces policies executed by the Open Policy Agent (OPA), a policy engine for Cloud Native environments hosted by Cloud Native Computing Foundation.

This document demonstrates how to use the Gatekeeper to manage OPA policies.

Prerequisites

Start up Karmada clusters

You just need to clone Karmada repo, and run the following script in the Karmada directory.

hack/local-up-karmada.sh

Gatekeeper Installations

In this case, you will use Gatekeeper v3.7.2. Related deployment files are from here.

Install Gatekeeper APIs on Karmada

Create resource objects for Gatekeeper in karmada controller plane, the content is as follows.

kubectl config use-context karmada-apiserver

Deploy namespace: https://github.com/open-policy-agent/gatekeeper/blob/release-3.7/deploy/gatekeeper.yaml#L1-L9

Deploy Gatekeeper CRDs: https://github.com/open-policy-agent/gatekeeper/blob/release-3.7/deploy/gatekeeper.yaml#L27-L1999

Deploy Gatekeeper secrets: https://github.com/open-policy-agent/gatekeeper/blob/release-3.7/deploy/gatekeeper.yaml#L2261-L2267

Deploy webhook config:

apiVersion: admissionregistration.k8s.io/v1
kind: MutatingWebhookConfiguration
metadata:
  labels:
    gatekeeper.sh/system: "yes"
  name: gatekeeper-mutating-webhook-configuration
webhooks:
  - admissionReviewVersions:
      - v1
      - v1beta1
    clientConfig:
      #Change the clientconfig from service type to url type cause webhook config and service are not in the same cluster.
      url: https://gatekeeper-webhook-service.gatekeeper-system.svc:443/v1/mutate
    failurePolicy: Ignore
    matchPolicy: Exact
    name: mutation.gatekeeper.sh
    namespaceSelector:
      matchExpressions:
        - key: admission.gatekeeper.sh/ignore
          operator: DoesNotExist
    rules:
      - apiGroups:
          - '*'
        apiVersions:
          - '*'
        operations:
          - CREATE
          - UPDATE
        resources:
          - '*'
    sideEffects: None
    timeoutSeconds: 1
---
apiVersion: admissionregistration.k8s.io/v1
kind: ValidatingWebhookConfiguration
metadata:
  labels:
    gatekeeper.sh/system: "yes"
  name: gatekeeper-validating-webhook-configuration
webhooks:
  - admissionReviewVersions:
      - v1
      - v1beta1
    clientConfig:
      #Change the clientconfig from service type to url type cause webhook config and service are not in the same cluster.
      url: https://gatekeeper-webhook-service.gatekeeper-system.svc:443/v1/admit
    failurePolicy: Ignore
    matchPolicy: Exact
    name: validation.gatekeeper.sh
    namespaceSelector:
      matchExpressions:
        - key: admission.gatekeeper.sh/ignore
          operator: DoesNotExist
    rules:
      - apiGroups:
          - '*'
        apiVersions:
          - '*'
        operations:
          - CREATE
          - UPDATE
        resources:
          - '*'
    sideEffects: None
    timeoutSeconds: 3
  - admissionReviewVersions:
      - v1
      - v1beta1
    clientConfig:
      #Change the clientconfig from service type to url type cause webhook config and service are not in the same cluster.
      url: https://gatekeeper-webhook-service.gatekeeper-system.svc:443/v1/admitlabel
    failurePolicy: Fail
    matchPolicy: Exact
    name: check-ignore-label.gatekeeper.sh
    rules:
      - apiGroups:
          - ""
        apiVersions:
          - '*'
        operations:
          - CREATE
          - UPDATE
        resources:
          - namespaces
    sideEffects: None
    timeoutSeconds: 3

You need to change the clientconfig from service type to url type for multi-cluster deployment.

Also, you need to deploy a dummy pod in gatekeeper-system namespace in karmada-apiserver context, because when Gatekeeper generates a policy template CRD, a status object is generated to monitor the status of the policy template, and the status object is bound by the controller Pod through the OwnerReference. Therefore, when the CRD and the controller are not in the same cluster, a dummy Pod needs to be used instead of the controller. The Pod enables the status object to be successfully generated.

For example:

apiVersion: v1
kind: Pod
metadata:
  name: dummy-pod
  namespace: gatekeeper-system
spec:
  containers:
  - name: dummy-pod
    image: nginx:latest
    imagePullPolicy: Always

Install GateKeeper components on host cluster

kubectl config use-context karmada-host

Deploy namespace: https://github.com/open-policy-agent/gatekeeper/blob/release-3.7/deploy/gatekeeper.yaml#L1-L9

Deploy RBAC resources for deployment: https://github.com/open-policy-agent/gatekeeper/blob/release-3.7/deploy/gatekeeper.yaml#L1999-L2375

Deploy Gatekeeper controllers and secret as kubeconfig:

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    control-plane: audit-controller
    gatekeeper.sh/operation: audit
    gatekeeper.sh/system: "yes"
  name: gatekeeper-audit
  namespace: gatekeeper-system
spec:
  replicas: 1
  selector:
    matchLabels:
      control-plane: audit-controller
      gatekeeper.sh/operation: audit
      gatekeeper.sh/system: "yes"
  template:
    metadata:
      annotations:
        container.seccomp.security.alpha.kubernetes.io/manager: runtime/default
      labels:
        control-plane: audit-controller
        gatekeeper.sh/operation: audit
        gatekeeper.sh/system: "yes"
    spec:
      automountServiceAccountToken: true
      containers:
        - args:
            - --operation=audit
            - --operation=status
            - --operation=mutation-status
            - --logtostderr
            - --disable-opa-builtin={http.send}
            - --kubeconfig=/etc/kubeconfig
          command:
            - /manager
          env:
            - name: POD_NAMESPACE
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: metadata.namespace
            - name: POD_NAME
              value: {{POD_NAME}}
          image: openpolicyagent/gatekeeper:v3.7.2
          imagePullPolicy: Always
          livenessProbe:
            httpGet:
              path: /healthz
              port: 9090
          name: manager
          ports:
            - containerPort: 8888
              name: metrics
              protocol: TCP
            - containerPort: 9090
              name: healthz
              protocol: TCP
          readinessProbe:
            httpGet:
              path: /readyz
              port: 9090
          resources:
            limits:
              cpu: 1000m
              memory: 512Mi
            requests:
              cpu: 100m
              memory: 256Mi
          securityContext:
            allowPrivilegeEscalation: false
            capabilities:
              drop:
                - all
            readOnlyRootFilesystem: true
            runAsGroup: 999
            runAsNonRoot: true
            runAsUser: 1000
          volumeMounts:
            - mountPath: /tmp/audit
              name: tmp-volume
            - mountPath: /etc/kubeconfig
              name: kubeconfig
              subPath: kubeconfig
      nodeSelector:
        kubernetes.io/os: linux
      priorityClassName: system-cluster-critical
      serviceAccountName: gatekeeper-admin
      terminationGracePeriodSeconds: 60
      volumes:
        - emptyDir: {}
          name: tmp-volume
        - name: kubeconfig
          secret:
            defaultMode: 420
            secretName: kubeconfig
---
apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    control-plane: controller-manager
    gatekeeper.sh/operation: webhook
    gatekeeper.sh/system: "yes"
  name: gatekeeper-controller-manager
  namespace: gatekeeper-system
spec:
  replicas: 3
  selector:
    matchLabels:
      control-plane: controller-manager
      gatekeeper.sh/operation: webhook
      gatekeeper.sh/system: "yes"
  template:
    metadata:
      annotations:
        container.seccomp.security.alpha.kubernetes.io/manager: runtime/default
      labels:
        control-plane: controller-manager
        gatekeeper.sh/operation: webhook
        gatekeeper.sh/system: "yes"
    spec:
      affinity:
        podAntiAffinity:
          preferredDuringSchedulingIgnoredDuringExecution:
            - podAffinityTerm:
                labelSelector:
                  matchExpressions:
                    - key: gatekeeper.sh/operation
                      operator: In
                      values:
                        - webhook
                topologyKey: kubernetes.io/hostname
              weight: 100
      automountServiceAccountToken: true
      containers:
        - args:
            - --port=8443
            - --logtostderr
            - --exempt-namespace=gatekeeper-system
            - --operation=webhook
            - --operation=mutation-webhook
            - --disable-opa-builtin={http.send}
            - --kubeconfig=/etc/kubeconfig
          command:
            - /manager
          env:
            - name: POD_NAMESPACE
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: metadata.namespace
            - name: POD_NAME
              value: {{POD_NAME}}
          image: openpolicyagent/gatekeeper:v3.7.2
          imagePullPolicy: Always
          livenessProbe:
            httpGet:
              path: /healthz
              port: 9090
          name: manager
          ports:
            - containerPort: 8443
              name: webhook-server
              protocol: TCP
            - containerPort: 8888
              name: metrics
              protocol: TCP
            - containerPort: 9090
              name: healthz
              protocol: TCP
          readinessProbe:
            httpGet:
              path: /readyz
              port: 9090
          resources:
            limits:
              cpu: 1000m
              memory: 512Mi
            requests:
              cpu: 100m
              memory: 256Mi
          securityContext:
            allowPrivilegeEscalation: false
            capabilities:
              drop:
                - all
            readOnlyRootFilesystem: true
            runAsGroup: 999
            runAsNonRoot: true
            runAsUser: 1000
          volumeMounts:
            - mountPath: /certs
              name: cert
              readOnly: true
            - mountPath: /etc/kubeconfig
              name: kubeconfig
              subPath: kubeconfig
      nodeSelector:
        kubernetes.io/os: linux
      priorityClassName: system-cluster-critical
      serviceAccountName: gatekeeper-admin
      terminationGracePeriodSeconds: 60
      volumes:
        - name: cert
          secret:
            defaultMode: 420
            secretName: gatekeeper-webhook-server-cert
        - name: kubeconfig
          secret:
            defaultMode: 420
            secretName: kubeconfig
---
apiVersion: policy/v1beta1
kind: PodDisruptionBudget
metadata:
  labels:
    gatekeeper.sh/system: "yes"
  name: gatekeeper-controller-manager
  namespace: gatekeeper-system
spec:
  minAvailable: 1
  selector:
    matchLabels:
      control-plane: controller-manager
      gatekeeper.sh/operation: webhook
      gatekeeper.sh/system: "yes"
---
apiVersion: v1
stringData:
  kubeconfig: |-
    apiVersion: v1
    clusters:
    - cluster:
        certificate-authority-data: {{ca_crt}}
        server: https://karmada-apiserver.karmada-system.svc.cluster.local:5443
      name: kind-karmada
    contexts:
    - context:
        cluster: kind-karmada
        user: kind-karmada
      name: karmada
    current-context: karmada
    kind: Config
    preferences: {}
    users:
    - name: kind-karmada
      user:
        client-certificate-data: {{client_cer}}
        client-key-data: {{client_key}}
kind: Secret
metadata:
  name: kubeconfig
  namespace: gatekeeper-system

You need to fill in the dummy pod created in step 1 to {{ POD_NAME }} and fill in the secret which represents kubeconfig pointing to karmada-apiserver.

Deploy ResourceQuota: https://github.com/open-policy-agent/gatekeeper/blob/release-3.7/deploy/gatekeeper.yaml#L10-L26

Extra steps

After all, we need to copy the secret gatekeeper-webhook-server-cert in karmada-apiserver context to that in karmada-host context to keep secrets stored in etcd and volumes mounted in controller the same.

Run demo

Create k8srequiredlabels template

apiVersion: templates.gatekeeper.sh/v1
kind: ConstraintTemplate
metadata:
  name: k8srequiredlabels
spec:
  crd:
    spec:
      names:
        kind: K8sRequiredLabels
      validation:
        openAPIV3Schema:  
          type: object
          description: Describe K8sRequiredLabels crd parameters
          properties:
            labels:
              type: array
              items:
                type: string
                description: A label 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("you must provide labels: %v", [missing])
        }

Create k8srequiredlabels constraint

apiVersion: constraints.gatekeeper.sh/v1beta1
kind: K8sRequiredLabels
metadata:
  name: ns-must-have-gk
spec:
  match:
    kinds:
      - apiGroups: [""]
        kinds: ["Namespace"]  
  parameters:
    labels: ["gatekeepers"]  

Create a bad namespace

kubectl create ns test
Error from server ([ns-must-have-gk] you must provide labels: {"gatekeepers"}): admission webhook "validation.gatekeeper.sh" denied the request: [ns-must-have-gk] you must provide labels: {"gatekeepers"}

Reference

https://github.com/open-policy-agent/gatekeeper

Prerequisites​

Start up Karmada clusters​

Gatekeeper Installations​

Install Gatekeeper APIs on Karmada​

Install GateKeeper components on host cluster​

Extra steps​

Run demo​

Create k8srequiredlabels template​

Create k8srequiredlabels constraint​

Create a bad namespace​

Reference​