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Preparing installation assets for iSCSI booting

You can boot an OpenShift Container Platform cluster through Internet Small Computer System Interface (iSCSI) by using an ISO image generated by the Agent-based Installer. The following procedures describe how to prepare the necessary installation resources to boot from an iSCSI target.

The assets you create in these procedures deploy a single-node OpenShift Container Platform installation. You can use these procedures as a basis and modify configurations according to your requirements.

Requirements for iSCSI booting

The following configurations are necessary to enable iSCSI booting when using the Agent-based Installer:

  • Dynamic Host Configuration Protocol (DHCP) must be configured. Static networking is not supported.

  • You must create an additional network for iSCSI that is separate from the machine network of the cluster. The machine network is rebooted during cluster installation and cannot be used for the iSCSI session.

  • If the host on which you are booting the agent ISO image also has an installed disk, it might be necessary to specify the iSCSI disk name in the rootDeviceHints parameter to ensure that it is chosen as the boot disk for the final Red Hat Enterprise Linux CoreOS (RHCOS) image. You can also use a diskless environment for iSCSI booting, in which case you do not need to set the rootDeviceHints parameter.

Additional resources

Prerequisites

Downloading the Agent-based Installer

Use this procedure to download the Agent-based Installer and the CLI needed for your installation.

Procedure

  1. Log in to the OpenShift Container Platform web console using your login credentials.

  2. Navigate to Datacenter.

  3. Click Run Agent-based Installer locally.

  4. Select the operating system and architecture for the OpenShift Installer and Command line interface.

  5. Click Download Installer to download and extract the install program.

  6. Download or copy the pull secret by clicking on Download pull secret or Copy pull secret.

  7. Click Download command-line tools and place the openshift-install binary in a directory that is on your PATH.

Creating the preferred configuration inputs

Use this procedure to create the preferred configuration inputs used to create the agent image.

Configuring the install-config.yaml and agent-config.yaml files is the preferred method for using the Agent-based Installer. Using GitOps ZTP manifests is optional.
Procedure

  1. Install the nmstate dependency by running the following command:

    $ sudo dnf install /usr/bin/nmstatectl -y

  2. Place the openshift-install binary in a directory that is on your PATH.

  3. Create a directory to store the install configuration by running the following command:

    $ mkdir ~/<directory_name>

  4. Create the install-config.yaml file by running the following command:

    $ cat << EOF > ./<directory_name>/install-config.yaml
apiVersion: v1
baseDomain: test.example.com
compute:
- architecture: amd64 (1)
  hyperthreading: Enabled
  name: worker
  replicas: 0
controlPlane:
  architecture: amd64
  hyperthreading: Enabled
  name: master
  replicas: 1
metadata:
  name: sno-cluster (2)
networking:
  clusterNetwork:
  - cidr: 10.128.0.0/14
    hostPrefix: 23
  machineNetwork:
  - cidr: 192.168.0.0/16
  networkType: OVNKubernetes (3)
  serviceNetwork:
  - 172.30.0.0/16
platform: (4)
  none: {}
pullSecret: '<pull_secret>' (5)
sshKey: '<ssh_pub_key>' (6)
EOF
    1 Specify the system architecture. Valid values are amd64, arm64, ppc64le, and s390x.

    If you are using the release image with the multi payload, you can install the cluster on different architectures such as arm64, amd64, s390x, and ppc64le. Otherwise, you can install the cluster only on the release architecture displayed in the output of the openshift-install version command. For more information, see "Verifying the supported architecture for installing an Agent-based Installer cluster".
    2 Required. Specify your cluster name.
    3 The cluster network plugin to install. The default value OVNKubernetes is the only supported value.
    4 Specify your platform.

    For bare-metal platforms, host settings made in the platform section of the install-config.yaml file are used by default, unless they are overridden by configurations made in the agent-config.yaml file.
    5 Specify your pull secret.
    6 Specify your SSH public key.

    If you set the platform to vSphere or baremetal, you can configure IP address endpoints for cluster nodes in three ways:

    • IPv4

    • IPv6

    • IPv4 and IPv6 in parallel (dual-stack)

    IPv6 is supported only on bare metal platforms.
    Example of dual-stack networking
    networking:
  clusterNetwork:
    - cidr: 172.21.0.0/16
      hostPrefix: 23
    - cidr: fd02::/48
      hostPrefix: 64
  machineNetwork:
    - cidr: 192.168.11.0/16
    - cidr: 2001:DB8::/32
  serviceNetwork:
    - 172.22.0.0/16
    - fd03::/112
  networkType: OVNKubernetes
platform:
  baremetal:
    apiVIPs:
    - 192.168.11.3
    - 2001:DB8::4
    ingressVIPs:
    - 192.168.11.4
    - 2001:DB8::5

    When you use a disconnected mirror registry, you must add the certificate file that you created previously for your mirror registry to the additionalTrustBundle field of the install-config.yaml file.

  5. Create the agent-config.yaml file by running the following command:

    $ cat > agent-config.yaml << EOF
apiVersion: v1beta1
kind: AgentConfig
metadata:
  name: sno-cluster
rendezvousIP: 192.168.111.80 (1)
hosts: (2)
  - hostname: master-0 (3)
    interfaces:
      - name: eno1
        macAddress: 00:ef:44:21:e6:a5
    rootDeviceHints: (4)
      deviceName: /dev/sdb
    networkConfig: (5)
      interfaces:
        - name: eno1
          type: ethernet
          state: up
          mac-address: 00:ef:44:21:e6:a5
          ipv4:
            enabled: true
            address:
              - ip: 192.168.111.80
                prefix-length: 23
            dhcp: false
      dns-resolver:
        config:
          server:
            - 192.168.111.1
      routes:
        config:
          - destination: 0.0.0.0/0
            next-hop-address: 192.168.111.2
            next-hop-interface: eno1
            table-id: 254
minimalISO: true (6)
EOF
    1 This IP address is used to determine which node performs the bootstrapping process as well as running the assisted-service component. You must provide the rendezvous IP address when you do not specify at least one host’s IP address in the networkConfig parameter. If this address is not provided, one IP address is selected from the provided hosts' networkConfig.
    2 Optional: Host configuration. The number of hosts defined must not exceed the total number of hosts defined in the install-config.yaml file, which is the sum of the values of the compute.replicas and controlPlane.replicas parameters.
    3 Optional: Overrides the hostname obtained from either the Dynamic Host Configuration Protocol (DHCP) or a reverse DNS lookup. Each host must have a unique hostname supplied by one of these methods.
    4 Enables provisioning of the Red Hat Enterprise Linux CoreOS (RHCOS) image to a particular device. The installation program examines the devices in the order it discovers them, and compares the discovered values with the hint values. It uses the first discovered device that matches the hint value.
    5 Optional: Configures the network interface of a host in NMState format.
    6 Generates an ISO image without the rootfs image file, and instead provides details about where to pull the rootfs file from. You must set this parameter to true to enable iSCSI booting.
Additional resources

Creating the installation files

Use the following procedure to generate the ISO image and create an iPXE script to upload to your iSCSI target.

Procedure

  1. Create the agent image by running the following command:

    $ openshift-install --dir <install_directory> agent create image

  2. Create an iPXE script by running the following command:

    $ cat << EOF > agent.ipxe
!ipxe
set initiator-iqn <iscsi_initiator_base>:\${hostname}
sanboot --keep iscsi:<iscsi_network_subnet>.1::::<iscsi_target_base>:\${hostname}
EOF

    where:

    <iscsi_initiator_base>

    Specifies the iSCSI initiator name on the host that is booting the ISO. This name can also be used by the iSCSI target.

    <iscsi_network_subnet>

    Specifies the IP address of the iSCSI target.

    <iscsi_target_base>

    Specifies the iSCSI target name. This name can be the same as the initiator name.

    Example Command
    $ cat << EOF > agent.ipxe
!ipxe
set initiator-iqn iqn.2023-01.com.example:\${hostname}
sanboot --keep iscsi:192.168.45.1::::iqn.2023-01.com.example:\${hostname}
EOF