Red Hat OpenShift Container Platform

On-cluster image mode known limitations

Note the following limitations when working with the on-cluster layering feature:

On-cluster image mode is not supported on multi-architecture compute machines.
Using multiple MachineOSConfig objects on the same machine config pool is not supported. You need a separate MachineOSConfig CR for each machine config pool where you want to use a distinct custom layered image.
If you scale up a machine set that uses a custom layered image, the nodes reboot two times. The first, when the node is initially created with the base image and a second time when the custom layered image is applied.
Node disruption policies are not supported on nodes with a custom layered image. However, the following machine configuration changes do not cause a new image build or the reboot of a node with an on-cluster custom layered image:
- Modifying the configuration files in the /var or /etc directory
- Adding or modifying a systemd service
- Changing SSH keys
- Removing mirroring rules from ICSP, ITMS, and IDMS objects
- Changing the trusted CA, by updating the user-ca-bundle configmap in the openshift-config namespace
The following machine configuration changes do cause a new image build and a node reboot:
- Changing the kernel arguments
- Changing the OSImageURL parameter
- Adding or removing extensions
The images used in creating custom layered images take up space in your push registry. Always be aware of the free space in your registry and prune the images as needed. You can automatically remove an on-cluster custom layered image from the repository by deleting the MachineOSBuild object that created the image. Note that the credentials provided by the registry push secret must also grant permission to delete an image from the registry. For more information, see "Removing an on-cluster custom layered image".