How to use policy groups

tip

Before working with Policy Groups, consult the explanation.

Using the example from the explanation of Policy Groups, use these commands to implement it.

kubectl apply -f group-policy-demo.yaml

A ClusterAdmissionPolicyGroup that rejects Pods that use images with the latest tag, unless the images are signed by two trusted parties: Alice and Bob.

apiVersion: policies.kubewarden.io/v1
kind: ClusterAdmissionPolicyGroup # or AdmissionPolicyGroup
metadata:
  name: demo
spec:
  rules:
    - apiGroups: [""]
      apiVersions: ["v1"]
      resources: ["pods"]
      operations:
        - CREATE
        - UPDATE
  policies:
    signed_by_alice:
      module: ghcr.io/kubewarden/policies/verify-image-signatures:v0.3.0
      settings:
        modifyImagesWithDigest: false
        signatures:
          - image: "*"
            pubKeys:
              - |
                -----BEGIN PUBLIC KEY-----
                MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEyg65hiNHt8FXTamzCn34IE3qMGcV
                yQz3gPlhoKq3yqa1GIofcgLjUZtcKlUSVAU2/S5gXqyDnsW6466Jx/ZVlg==
                -----END PUBLIC KEY-----
    signed_by_bob:
      module: ghcr.io/kubewarden/policies/verify-image-signatures:v0.3.0
      settings:
        modifyImagesWithDigest: false
        signatures:
          - image: "*"
            pubKeys:
              - |
                -----BEGIN PUBLIC KEY-----
                MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEswA3Ec4w1ErOpeLPfCdkrh8jvk3X
                urm8ZrXi4S3an70k8bf1OlGnI/aHCcGleewHbBk1iByySMwr8BabchXGSg==
                -----END PUBLIC KEY-----
    reject_latest:
      module: registry://ghcr.io/kubewarden/policies/trusted-repos:v0.2.0
      settings:
        tags:
          reject:
            - latest
  expression: "reject_latest() || (signed_by_alice() && signed_by_bob())"
  message: "the image is using the latest tag or is not signed by Alice and Bob"

Once the policy is active, the creation of a non-compliant Pod will be rejected. To obtain more information about the evaluation of the policies that are part of the group, increase the vebosity level of kubectl:

kubectl -v4 apply -f signed-pod.yml
I0919 18:29:40.251332    4330 helpers.go:246] server response object: [{
  "kind": "Status",
  "apiVersion": "v1",
  "metadata": {},
  "status": "Failure",
  "message": "error when creating \"signed-pod.yml\": admission webhook \"clusterwide-demo.kubewarden.admission\" denied the request: the image is using the latest tag or is not signed by Alice and Bob",
  "details": {
    "causes": [
      {
        "message": "Resource signed is not accepted: verification of image testing.registry.svc.lan/busybox:latest failed: Host error: Callback evaluation failure: Image verification failed: missing signatures\nThe following constraints were not satisfied:\nkind: pubKey\nowner: null\nkey: |\n  -----BEGIN PUBLIC KEY-----\n  MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEswA3Ec4w1ErOpeLPfCdkrh8jvk3X\n  urm8ZrXi4S3an70k8bf1OlGnI/aHCcGleewHbBk1iByySMwr8BabchXGSg==\n  -----END PUBLIC KEY-----\nannotations: null\n",
        "field": "spec.policies.signed_by_bob"
      },
      {
        "message": "not allowed, reported errors: tags not allowed: latest",
        "field": "spec.policies.reject_latest"
      }
    ]
  },
  "code": 400
}]
Error from server: error when creating "signed-pod.yml": admission webhook "clusterwide-demo.kubewarden.admission" denied the request: the image is using the latest tag or is not signed by Alice and Bob

note

The evaluation output produced by the policies that are part of the group is visible only by increasing the verbosity level of kubectl.

A verbosity level of 4 is enough to see the evaluation output of the policies.