Chapter 9. Installing on a single node

9.1. Preparing to install on a single node

9.1.1. Prerequisites

9.1.2. About OpenShift on a single node

You can create a single node cluster with standard installation methods. OpenShift Container Platform on a single node is a specialized installation that requires the creation of a special ignition configuration ISO. The primary use case is for edge computing workloads, including intermittent connectivity, portable clouds, and 5G radio access networks (RAN) close to a base station. The major tradeoff with an installation on a single node is the lack of high availability.

9.1.3. Requirements for installing OpenShift on a single node

Installing OpenShift Container Platform on a single node alleviates some of the requirements for high availability and large scale clusters. However, you must address the following requirements:

  • Administration host: You must have a computer to prepare the ISO, to create the USB boot drive, and to monitor the installation.
  • Bare metal installation: Installing OpenShift Container Platform on a single node on bare metal requires that you specify the platform.none: {} parameter in the install-config.yaml configuration file.
  • Production-grade server: Installing OpenShift Container Platform on a single node requires a server with sufficient resources to run OpenShift Container Platform services and a production workload.

    Table 9.1. Minimum resource requirements

    ProfilevCPUMemoryStorage

    Minimum

    8 vCPU cores

    32GB of RAM

    120GB

    Note

    One vCPU is equivalent to one physical core when simultaneous multithreading (SMT), or hyperthreading, is not enabled. When enabled, use the following formula to calculate the corresponding ratio:

    (threads per core × cores) × sockets = vCPUs

    The server must have a Baseboard Management Controller (BMC) when booting with virtual media.

  • Networking: The server must have access to the internet or access to a local registry if it is not connected to a routable network. The server must have a DHCP reservation or a static IP address for the Kubernetes API, Ingress route, and cluster node domain names. You must configure the DNS to resolve the IP address to each of the following fully qualified domain names (FQDN):

    Table 9.2. Required DNS records

    UsageFQDNDescription

    Kubernetes API

    api.<cluster_name>.<base_domain>

    Add a DNS A/AAAA or CNAME record. This record must be resolvable by clients external to the cluster.

    Internal API

    api-int.<cluster_name>.<base_domain>

    Add a DNS A/AAAA or CNAME record when creating the ISO manually. This record must be resolvable by nodes within the cluster.

    Ingress route

    *.apps.<cluster_name>.<base_domain>

    Add a wildcard DNS A/AAAA or CNAME record that targets the node. This record must be resolvable by clients external to the cluster.

    Cluster node

    <hostname>.<cluster_name>.<base_domain>

    Add a DNS A/AAAA or CNAME record and DNS PTR record to identify the node.

    Without persistent IP addresses, communications between the apiserver and etcd might fail.

9.2. Installing OpenShift on a single node

9.2.1. Generating the discovery ISO with the Assisted Installer

Installing OpenShift Container Platform on a single node requires a discovery ISO, which the Assisted Installer (AI) can generate with the cluster name, base domain, Secure Shell (SSH) public key, and pull secret.

Procedure

  1. On the administration node, open a browser and navigate to Install OpenShift with the Assisted Installer.
  2. Click Create Cluster to create a new cluster.
  3. In the Cluster name field, enter a name for the cluster.
  4. In the Base domain field, enter a base domain. For example:

    example.com

    All DNS records must be subdomains of this base domain and include the cluster name. You cannot change the base domain after cluster installation. For example:

    <cluster-name>.example.com
  5. Select Install single node OpenShift (SNO).
  6. Read the limitations for installing OpenShift Container Platform on a single node.
  7. Select the OpenShift Container Platform version.
  8. Optional: Edit the pull secret.
  9. Click Next.
  10. Click Generate Discovery ISO.
  11. Select Full image file to boot with a USB drive or PXE. Select Minimal image file to boot with virtual media.
  12. Add SSH public key of the administration node to the Public key field.
  13. Click Generate Discovery ISO.
  14. Download the discovery ISO.
  15. Make a note of the discovery ISO URL for installing with virtual media.

9.2.2. Generating the discovery ISO manually

Installing OpenShift Container Platform on a single node requires a discovery ISO, which you can generate with the following procedure.

Procedure

  1. Download the OpenShift Container Platform client (oc) and make it available for use by entering the following command:

    $ curl -k https://mirror.openshift.com/pub/openshift-v4/clients/ocp/latest/openshift-client-linux.tar.gz > oc.tar.gz
    $ tar zxf oc.tar.gz
    $ chmod +x oc
  2. Set the OpenShift Container Platform version:

    $ OCP_VERSION=<ocp_version> 1
    1
    Replace <ocp_version> with the current version. For example. latest-4.9
  3. Download the OpenShift Container Platform installer and make it available for use by entering the following commands:

    $ curl -k https://mirror.openshift.com/pub/openshift-v4/clients/ocp/$OCP_VERSION/openshift-install-linux.tar.gz > openshift-install-linux.tar.gz
    $ tar zxvf openshift-install-linux.tar.gz
    $ chmod +x openshift-install
  4. Retrieve the RHCOS ISO URL:

    $ ISO_URL=$(./openshift-install coreos print-stream-json | grep location | grep x86_64 | grep iso | cut -d\" -f4)
  5. Download the RHCOS ISO:

    $ curl $ISO_URL > rhcos-live.x86_64.iso
  6. Prepare the install-config.yaml file:

    apiVersion: v1
    baseDomain: <domain> 1
    compute:
    - name: worker
      replicas: 0 2
    controlPlane:
      name: master
      replicas: 1 3
    metadata:
      name: <name> 4
    networking:
      networkType: OVNKubernetes
      clusterNetwork:
      - cidr: <IP_address>/<prefix> 5
        hostPrefix: <prefix> 6
      serviceNetwork:
      - <IP_address>/<prefix> 7
    platform:
      none: {}
    BootstrapInPlace:
      InstallationDisk: <path_to_install_drive> 8
    pullSecret: '<pull_secret>' 9
    sshKey: |
      <ssh_key> 10
    1
    Add the cluster domain name.
    2
    Set the compute replicas to 0. This makes the control plane node schedulable.
    3
    Set the controlPlane replicas to 1. In conjunction with the previous compute setting, this setting ensures the cluster runs on a single node.
    4
    Set the metadata name to the cluster name.
    5
    Set the clusterNetwork CIDR.
    6
    Set the clusterNetwork host prefix. Pods receive their IP addresses from this pool.
    7
    Set the serviceNetwork CIDR. Services receive their IP addresses from this pool.
    8
    Set the path to the installation disk drive.
    9
    Copy the pull secret from Red Hat Hybrid Cloud Console. In step 1, click Download pull secret and add the contents to this configuration setting.
    10
    Add the public SSH key from the administration host so that you can log in to the cluster after installation.
  7. Generate OpenShift Container Platform assets:

    $ mkdir ocp
    $ cp install-config.yaml ocp
    $ ./openshift-install --dir=ocp create single-node-ignition-config
  8. Embed the ignition data into the RHCOS ISO:

    $ alias coreos-installer='podman run --privileged --rm \
            -v /dev:/dev -v /run/udev:/run/udev -v $PWD:/data \
            -w /data quay.io/coreos/coreos-installer:release'
    $ cp ocp/bootstrap-in-place-for-live-iso.ign iso.ign
    $ coreos-installer iso ignition embed -fi iso.ign rhcos-live.x86_64.iso

9.2.3. Installing with USB media

Installing with USB media involves creating a bootable USB drive with the discovery ISO on the administration node. Booting the server with the USB drive prepares the node for a single node installation.

Procedure

  1. On the administration node, insert a USB drive into a USB port.
  2. Create a bootable USB drive:

    # dd if=<path-to-iso> of=<path/to/usb> status=progress

    For example:

    # dd if=discovery_image_sno.iso of=/dev/sdb status=progress

    After the ISO is copied to the USB drive, you can use the USB drive to install OpenShift Container Platform.

  3. On the server, insert the USB drive into a USB port.
  4. Reboot the server and enter the BIOS settings upon reboot.
  5. Change boot drive order to make the USB drive boot first.
  6. Save and exit the BIOS settings. The server will boot with the discovery image.

9.2.4. Monitoring the installation with the Assisted Installer

If you created the ISO using the Assisted Installer, use this procedure to monitor the installation.

Procedure

  1. On the administration host, return to the browser and refresh the page. If necessary, reload the Install OpenShift with the Assisted Installer page and select the cluster name.
  2. Click Next until you reach step 3, Networking.
  3. Select a subnet from the available subnets.
  4. Keep Use the same host discovery SSH key checked. You can change the SSH public key, if necessary.
  5. Click Next to proceed to the Review and Create step.
  6. Click Install cluster.
  7. Monitor the installation’s progress. Watch the cluster events. After the installation process finishes writing the discovery image to the server’s drive, the server will restart. Remove the USB drive and reset the BIOS to boot to the server’s local media rather than the USB drive.

The server will restart several times, deploying the control plane.

9.2.5. Monitoring the installation manually

If you created the ISO manually, use this procedure to monitor the installation.

Procedure

  1. Monitor the installation:

    $ ./openshift-install --dir=ocp wait-for install-complete

    The server will restart several times while deploying the control plane.

  2. Optional: After the installation is complete, check the environment:

    $ export KUBECONFIG=ocp/auth/kubeconfig
    $ oc get nodes
    $ oc get clusterversion