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Chapter 9. Image Policy
9.1. 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
9.2. Configuring the ImagePolicy Admission Plug-in
To enable this feature, configure the plug-in in master-config.yaml:
Example 9.1. 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- 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.
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.
9.3. Testing the ImagePolicy Admission Plug-in
Use the
openshift/image-policy-checkto test your configuration.For example, use the information above, then test like this:
oc import-image openshift/image-policy-check:latest --confirm
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: firstCreate 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: firstCreate 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: firstCreate 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: firstGet the digest from
oc get istag/image-policy-check:latestand use it foroc annotate images/<digest> images.openshift.io/deny-execution=true. For example:$ oc annotate images/sha256:09ce3d8b5b63595ffca6636c7daefb1a615a7c0e3f8ea68e5db044a9340d6ba8 images.openshift.io/deny-execution=true
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
