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Chapter 5. Pinning images to nodes

A slow, unreliable connection to an image registry can interfere with operations that require pulling images, such as updating a cluster or deploying an application. This can include clusters that have low bandwidth, clusters with unreliable internet connectivity, or clusters in a disconnected environment. For example, a cluster update might require pulling more than one hundred images. Failure to pull those images could cause retries that can interfere with the update process and might cause the update to fail.

One way to prevent this is to pull the required images in advance, before they are actually needed, and pinning those images to a specific machine config pool (MCP). This ensures that the images are available to your nodes when needed. Pinned images can provide a more consistent update, which is important when scheduling updates into maintenance windows.

Pinned images also ensures that the images are available when deploying applications, so that you can deploy in a more reliable manner.

You can pin images to specific nodes by using a PinnedImageSet custom resource (CR), as described in Pinning images. Pinned images are stored on the nodes in the /etc/crio/crio.conf.d/50-pinned-images file on those nodes. The contents of the file appear similar to the following example: 

[crio]
  [crio.image]
    pinned_images = ["quay.io/openshift-release-dev/ocp-release@sha256:4198606580b69c8335ad7ae531c3a74e51aee25db5faaf368234e8c8dae5cbea", "quay.io/openshift-release-dev/ocp-release@sha256:513cf1028aa1a021fa73d0601427a0fbcf6d212b88aaf9d76d4e4841a061e44e", "quay.io/openshift-release-dev/ocp-release@sha256:61eae2d261e54d1b8a0e05f6b5326228b00468364563745eed88460af04f909b"]
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Another benefit to pinned images is that image garbage collection does not remove the pinned images.

Before pulling the images, the Machine Config Operator (MCO) verifies that there is enough storage space available on each affected node. If the node has sufficient space, the MCO creates the pinned image file, pulls the images, and reloads CRI-O. If there is not sufficient space, the MCO does not pull the images and presents an error message.

5.1. Pinning images
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You can pin images to your nodes by using a PinnedImageSet custom resource (CR). The pinned image set defines the list of images to pre-load and the machine config pool to which the images should be pinned.

The images are stored in the the /etc/crio/crio.conf.d/50-pinned-images file on the nodes.

Procedure

  1. Create a YAML file that defines the PinnedImageSet object, similar to the following example: 

    apiVersion: machineconfiguration.openshift.io/v1
kind: PinnedImageSet
metadata:
  labels:
    1 
    
    machineconfiguration.openshift.io/role: worker
  name: worker-pinned-images
spec:
  pinnedImages:
    2 
    
   - name: quay.io/openshift-release-dev/ocp-release@sha256:513cf1028aa1a021fa73d0601427a0fbcf6d212b88aaf9d76d4e4841a061e44e
   - name: quay.io/openshift-release-dev/ocp-release@sha256:61eae2d261e54d1b8a0e05f6b5326228b00468364563745eed88460af04f909b
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    where:

    labels
    Specifies an optional node selector to specify the machine config pool to pin the images to. If not specified, the images are pinned to all nodes in the cluster.
    pinnedImages
    Specifies a list of one or more images to pre-load.

  2. Create the PinnedImageSet object by running the following command: 

    $ oc create -f <file_name>.yaml
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Verification

  • Check that the pinned image set is reported in the machine config node object for the affected machine config pool by running the following command: 

    $ oc describe machineconfignode <machine_config_node_name>
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    Example command

    $ oc describe machineconfignode ci-ln-25hlkvt-72292-jrs48-worker-a-2bdj
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    Example output for a successful image pull and pin

    apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfigNode
metadata:
  creationTimestamp: "2025-04-28T18:40:29Z"
  generation: 3
  name: <machine_config_node_name>
# ...
status
  pinnedImageSets:
  - currentGeneration: 1
    desiredGeneration: 1
    name: worker-pinned-images
    1
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    1 1
    The PinnedImageset object is associated with the machine config node.

    Any failures or error messages would appear in the MachineConfigNode object status fields, as shown in the following example:

    Example output for a failed image pull and pin

    apiVersion: machineconfiguration.openshift.io/v1
kind: MachineConfigNode
metadata:
  creationTimestamp: "2025-04-28T18:40:29Z"
  generation: 3
  name: <machine_config_node_name>
# ...
  - lastTransitionTime: "2025-04-29T19:37:23Z"
    message: One or more PinnedImageSet is experiencing an error. See PinnedImageSet
      list for more details
    reason: PrefetchFailed
    status: "True"
    type: PinnedImageSetsDegraded
  configVersion:
    current: rendered-worker-cef1b52c532e19a20add12e369261fba
    desired: rendered-worker-cef1b52c532e19a20add12e369261fba
  observedGeneration: 3
  pinnedImageSets:
  - desiredGeneration: 1
    lastFailedGeneration: 1
    lastFailedGenerationError: 'failed to execute podman manifest inspect for "quay.io/rh-ee/machine-config-operator@sha256:65d3a308767b1773b6e3499dde6ef085753d7e20e685f78841079":
      exit status 125'
    name: worker-pinned-images
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  • Check that the pinned image file is created and contains the correct images.

    1. Start a debug session for a node by running the following command: 

      $ oc debug node/<node_name>
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    2. Set /host as the root directory within the debug shell by running the following command: 

      sh-5.1# chroot /host
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    3. Verify the contents of the pinned image file by running the following command: 

      $ cat /etc/crio/crio.conf.d/50-pinned-images
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      Example output

      [crio]
  [crio.image]
    pinned_images = ["quay.io/openshift-release-dev/ocp-release@sha256:4198606580b69c8335ad7ae531c3a74e51aee25db5faaf368234e8c8dae5cbea", "quay.io/openshift-release-dev/ocp-release@sha256:513cf1028aa1a021fa73d0601427a0fbcf6d212b88aaf9d76d4e4841a061e44e", "quay.io/openshift-release-dev/ocp-release@sha256:61eae2d261e54d1b8a0e05f6b5326228b00468364563745eed88460af04f909b"]
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      where:

      pinnedImages
      Specifies the images that have been pulled and pinned for the affected machine config pool.
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