About boot image management
With boot image management enabled, the Machine Config Operator (MCO) manages and updates the Red Hat Enterprise Linux CoreOS (RHCOS) version of the boot image in the machine sets for your control plane or worker nodes. This means that the MCO updates the boot image whenever you update your cluster. Without boot image management enabled, if your cluster was originally created with an older OpenShift Container Platform version, the boot image that the MCO would use to create new nodes is an older Red Hat Enterprise Linux CoreOS (RHCOS) version, even if your cluster is at a later OpenShift Container Platform version.
New nodes created after enabling the feature use the updated boot image. This feature has no effect on existing nodes.
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The following table lists the platforms on which boot image management is available:
For all other platforms, the MCO does not automatically update the boot image with each cluster update. Images from the Google Cloud Marketplace or AWS Marketplace are not automatically updated. For clusters where automatic updates are disabled or not supported, you can manually update the boot image on your cluster. See "Manually updating the boot image" for information. The method to update or specify the image varies by platform. |
For example, with the feature disabled, if your cluster was originally created with OpenShift Container Platform 4.16, the boot image that the MCO would use to create new nodes is the same RHCOS version that was installed for the cluster, even if your cluster is currently at a later OpenShift Container Platform version.
Using an older boot image could cause the following issues:
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Extra time to start nodes
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Certificate expiration issues
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Version skew issues
You can disable the boot image management feature, if needed. When the feature is disabled, the boot image version no longer updates with the cluster. For example, you could disable the boot image management feature in order to use a custom boot image that you do not want changed. For information on how to disable this feature, see "Disabling boot image management". If you disable this feature, you can re-enable the feature at any time. For information, see "Enabling boot image management".
How the cluster behaves after disabling or re-enabling the feature, depends upon when you made the change, including the following scenarios:
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If you disable the feature before updating to a new OpenShift Container Platform version:
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The boot image version used by the machine sets remains the same OpenShift Container Platform version as when the feature was disabled.
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When you scale up nodes, the new nodes use that same OpenShift Container Platform version.
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If you disable the feature after updating to a new OpenShift Container Platform version:
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The boot image version used by the machine sets is updated to match the updated OpenShift Container Platform version.
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When you scale up nodes, the new nodes use the updated OpenShift Container Platform version.
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If you update to a later OpenShift Container Platform version, the boot image version in the machine sets remains at the current version and is not updated with the cluster.
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If you enable the feature after disabling:
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The boot image version used by the machine sets is updated to the current OpenShift Container Platform version, if different.
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When you scale up nodes, the new nodes use the current OpenShift Container Platform version in the cluster.
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Because a boot image is used only when a node is scaled up, this feature has no effect on existing nodes. |
To view the current Red Hat Enterprise Linux CoreOS (RHCOS) boot image version used in your cluster, you can view the /sysroot/.coreos-aleph-version.json file on that node.
{
# ...
"ref": "docker://ostree-image-signed:oci-archive:/rhcos-418.94.202511191518-0-ostree.x86_64.ociarchive",
"version": "418.94.202511191518-0"
}where:
<version>-
Specifies the Red Hat Enterprise Linux CoreOS (RHCOS) boot image version. In this example, the boot image is from the originally-installed OpenShift Container Platform 4.18 version, regardless of the current version of the cluster.
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If any of the machine sets for which you want to enable boot image management use a
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