Overview

You can control which images are allowed to run on your cluster using the ImagePolicy admission plug-in (currently considered beta). It allows you to control:

  • The source of images: which registries can be used to pull images

  • Image resolution: force pods to run with immutable digests to ensure the image does not change due to a re-tag

  • Container image label restrictions: force an image to have or not have particular labels

  • Image annotation restrictions: force an image in the integrated container registry to have or not have particular annotations

Configuring the ImagePolicy Admission Plug-in

To enable this feature, configure the plug-in in master-config.yaml:

Example 1. Annotated Example File
admissionConfig:
  pluginConfig:
    openshift.io/ImagePolicy:
      configuration:
        kind: ImagePolicyConfig
        apiVersion: v1
        resolveImages: AttemptRewrite (1)
        executionRules: (2)
        - name: execution-denied
          # Reject all images that have the annotation images.openshift.io/deny-execution set to true.
          # This annotation may be set by infrastructure that wishes to flag particular images as dangerous
          onResources: (3)
          - resource: pods
          - resource: builds
          reject: true (4)
          matchImageAnnotations: (5)
          - key: images.openshift.io/deny-execution
            value: "true"
          skipOnResolutionFailure: true (6)
        - name: allow-images-from-internal-registry
          # allows images from the internal registry and tries to resolve them
          onResources:
          - resource: pods
          - resource: builds
          matchIntegratedRegistry: true
        - name: allow-images-from-dockerhub
          onResources:
          - resource: pods
          - resource: builds
          matchRegistries:
          - docker.io
        resolutionRules: (7)
        - targetResource:
            resource: pods
          localNames: true
        - targetResource: (8)
            group: batch
            resource: jobs
          localNames: true (9)
1 Try to resolve images to an immutable image digest and update the image pull specification in the pod.
2 Array of rules to evaluate against incoming resources. If you only have reject==true rules, the default is allow all. If you have any accept rule, the default is deny all.
3 Indicates which resources to enforce rules upon. If nothing is specified, the default is pods.
4 Indicates that if this rule matches, the pod should be rejected.
5 List of annotations to match on the image object’s metadata.
6 If you are not able to resolve the image, do not fail the pod.
7 Array of rules allowing use of image streams in Kubernetes resources. By default, this will allow pods, replication controllers, replica sets, deployments, and jobs to use image streams.
8 Identifies the group and resource for image stream resolution. If resource is *, this rule will apply to all resources in that group.
9 LocalNames will allow single segment names to be interpreted as namespace-local image stream tags, but only if the target image stream tag has the resolveLocalNames field set.

If you normally rely on infrastructure images being pulled using a default registry prefix (such as docker.io or registry.access.redhat.com), those images will not match to any matchRegistries value since they will have no registry prefix. To ensure infrastructure images have a registry prefix that can match your image policy, set the imageConfig.format value in your master-config.yaml file.

Testing the ImagePolicy Admission Plug-in

  1. Use the openshift/image-policy-check to test your configuration.

    For example, use the information above, then test like this:

    oc import-image openshift/image-policy-check:latest --confirm
  2. Create a pod using this YAML. The pod should be created.

    apiVersion: v1
    kind: Pod
    metadata:
      generateName: test-pod
    spec:
      containers:
      - image: docker.io/openshift/image-policy-check:latest
        name: first
  3. Create another pod pointing to a different registry. The pod should be rejected.

    apiVersion: v1
    kind: Pod
    metadata:
      generateName: test-pod
    spec:
      containers:
      - image: different-registry/openshift/image-policy-check:latest
        name: first
  4. Create a pod pointing to the internal registry using the imported image. The pod should be created and if you look at the image specification, you should see a digest in place of the tag.

    apiVersion: v1
    kind: Pod
    metadata:
      generateName: test-pod
    spec:
      containers:
      - image: <internal registry IP>:5000/<namespace>/image-policy-check:latest
        name: first
  5. Create a pod pointing to the internal registry using the imported image. The pod should be created and if you look at the image specification, you should see the tag unmodified.

    apiVersion: v1
    kind: Pod
    metadata:
      generateName: test-pod
    spec:
      containers:
      - image: <internal registry IP>:5000/<namespace>/image-policy-check:v1
        name: first
  6. Get the digest from oc get istag/image-policy-check:latest and use it for oc annotate images/<digest> images.openshift.io/deny-execution=true. For example:

    $ oc annotate images/sha256:09ce3d8b5b63595ffca6636c7daefb1a615a7c0e3f8ea68e5db044a9340d6ba8 images.openshift.io/deny-execution=true
  7. Create this pod again, and you should see the pod rejected:

    apiVersion: v1
    kind: Pod
    metadata:
      generateName: test-pod
    spec:
      containers:
      - image: <internal registry IP>:5000/<namespace>/image-policy-check:latest
        name: first