Create RHCOS machines by using an ISO image

To scale your Red Hat OpenShift Container Platform bare metal cluster, you can create more Red Hat Enterprise Linux CoreOS (RHCOS) compute machines by using an ISO image.

Prerequisites

  • You have obtained the URL of the Ignition config file for the compute machines for your cluster. You uploaded this file to your HTTP server during installation.

  • You must have the OpenShift CLI (oc) installed.

Procedure

  1. Extract the Ignition config file from the cluster by running the following command:

    $ oc extract -n openshift-machine-api secret/worker-user-data-managed --keys=userData --to=- > worker.ign

  2. Upload the worker.ign Ignition config file you exported from your cluster to your HTTP server. Note the URLs of these files.

  3. You can validate that the ignition files are available on the URLs. The following example gets the Ignition config files for the compute node:

    $ curl -k http://<HTTP_server>/worker.ign

  4. You can access the ISO image for booting your new machine by running the following command:

    RHCOS_VHD_ORIGIN_URL=$(oc -n openshift-machine-config-operator get configmap/coreos-bootimages -o jsonpath='{.data.stream}' | jq -r '.architectures.<architecture>.artifacts.metal.formats.iso.disk.location')

  5. Use the ISO file to install RHCOS on more compute machines. Use the same method that you used when you created machines before you installed the cluster:

    • Burn the ISO image to a disk and boot it directly.

    • Use ISO redirection with a LOM interface.

  6. Boot the RHCOS ISO image without specifying any options, or interrupting the live boot sequence. Wait for the installer to boot into a shell prompt in the RHCOS live environment.

    Note

    You can interrupt the RHCOS installation boot process to add kernel arguments. However, for this ISO procedure you must use the coreos-installer command as outlined in the following steps, instead of adding kernel arguments.

  7. Run the coreos-installer command by using sudo. The core user does not have the root privileges required to perform the installation. Specify the options that meet your installation requirements. At a minimum, you must specify the URL that points to the Ignition config file for the node type, and the device that you are installing to.

    $ sudo coreos-installer install --ignition-url=http://<HTTP_server>/<node_type>.ign <device> --ignition-hash=sha512-<digest>

    where:

    <digest>

    Specifies the Ignition config file SHA512 digest obtained through an HTTP URL to validate the authenticity of the Ignition config file on the cluster node.

    Note

    If you want to provide your Ignition config files through an HTTPS server that uses TLS, you can add the internal certificate authority (CA) to the system trust store before running coreos-installer.

    The following example initializes a compute node installation to the /dev/sda device. The Ignition config file for the compute node is obtained from an HTTP web server with the IP address 192.168.1.2:

    $ sudo coreos-installer install --ignition-url=http://192.168.1.2:80/installation_directory/worker.ign /dev/sda --ignition-hash=sha512-a5a2d43879223273c9b60af66b44202a1d1248fc01cf156c46d4a79f552b6bad47bc8cc78ddf0116e80c59d2ea9e32ba53bc807afbca581aa059311def2c3e3b

  8. Monitor the progress of the RHCOS installation on the console of the machine.

    Important

    Ensure that the installation is successful on each node before commencing with the Red Hat OpenShift Container Platform installation. Observing the installation process can also help to determine the cause of RHCOS installation issues that might arise.

  9. Continue to create more compute machines for your cluster.

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