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mco-update-boot-images.adoc

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Updated boot images

The Machine Config Operator (MCO) uses a boot image to start a {op-system-first} node. By default, {product-title} does not manage the boot image.

This means that the boot image in your cluster is not updated along with your cluster. For example, if your cluster was originally created with {product-title} 4.12, the boot image that the cluster uses to create nodes is the same 4.12 version, even if your cluster is at a later version. If the cluster is later upgraded to 4.13 or later, new nodes continue to scale with the same 4.12 image.

This process could cause the following issues:

  • Extra time to start nodes

  • Certificate expiration issues

  • Version skew issues

To avoid these issues, you can configure your cluster to update the boot image whenever you update your cluster. By modifying the MachineConfiguration object, you can enable this feature. Currently, the ability to update the boot image is available for only Google Cloud Platform (GCP) clusters and as a Technology Preview feature for Amazon Web Services (AWS) clusters. It is not supported for clusters managed by the {cluster-capi-operator}.

If you are not using the default user data secret, named worker-user-data, in your machine set, or you have modified the worker-user-data secret, you should not use managed boot image updates. This is because the Machine Config Operator (MCO) updates the machine set to use a managed version of the secret. By using the managed boot images feature, you are giving up the capability to customize the secret stored in the machine set object.

To view the current boot image used in your cluster, examine a machine set:

Example machine set with the boot image reference
apiVersion: machine.openshift.io/v1beta1
kind: MachineSet
metadata:
  name: ci-ln-hmy310k-72292-5f87z-worker-a
  namespace: openshift-machine-api
spec:
# ...
  template:
# ...
    spec:
# ...
      providerSpec:
# ...
        value:
          disks:
          - autoDelete: true
            boot: true
            image: projects/rhcos-cloud/global/images/rhcos-412-85-202203181601-0-gcp-x86-64 (1)
# ...

  1. This boot image is the same as the originally-installed {product-title} version, in this example {product-title} 4.12, regardless of the current version of the cluster. The way that the boot image is represented in the machine set depends on the platform, as the structure of the providerSpec field differs from platform to platform.

If you configure your cluster to update your boot images, the boot image referenced in your machine sets matches the current version of the cluster.