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image_policy.adoc

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Image Policy

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.

Note

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