Chapter 12. Installing on a single node
12.1. Preparing to install on a single node
12.1.1. Prerequisites
- You reviewed details about the OpenShift Container Platform installation and update processes.
- You have read the documentation on selecting a cluster installation method and preparing it for users.
12.1.2. 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.
The use of OpenShiftSDN with single-node OpenShift is deprecated. OVN-Kubernetes is the default networking solution for single-node OpenShift deployments.
12.1.3. 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.
-
Supported platforms: Installing OpenShift Container Platform on a single node is supported on bare metal and Certified third-party hypervisors. In all cases, you must specify the
platform.none: {}
parameter in theinstall-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 12.1. Minimum resource requirements Profile vCPU Memory Storage Minimum
8 vCPU cores
16GB of RAM
120GB
NoteOne 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 12.2. Required DNS records Usage FQDN Description 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.
Without persistent IP addresses, communications between the
apiserver
andetcd
might fail.
12.2. Installing OpenShift on a single node
12.2.1. 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
- On the administration node, open a browser and navigate to Install OpenShift with the Assisted Installer.
- Click Create Cluster to create a new cluster.
- In the Cluster name field, enter a name for the cluster.
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
- Select Install single node OpenShift (SNO).
- Read the 4.10 release notes, which outline some of the limitations for installing OpenShift Container Platform on a single node.
- Select the OpenShift Container Platform version.
- Optional: Edit the pull secret.
- Click Next.
- Click Generate Discovery ISO.
- Select Full image file to boot with a USB drive or PXE. Select Minimal image file to boot with virtual media.
- Add SSH public key of the administration node to the Public key field.
- Click Generate Discovery ISO.
- Download the discovery ISO.
- Make a note of the discovery ISO URL for installing with virtual media.
If you enable OpenShift Virtualization during this process, you must have a second local storage device of at least 50GiB for your virtual machines.
Additional resources
12.2.2. 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
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
Set the OpenShift Container Platform version:
$ OCP_VERSION=<ocp_version> 1
- 1
- Replace
<ocp_version>
with the current version. For example.latest-4.10
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
Retrieve the RHCOS ISO URL:
$ ISO_URL=$(./openshift-install coreos print-stream-json | grep location | grep x86_64 | grep iso | cut -d\" -f4)
Download the RHCOS ISO:
$ curl -L $ISO_URL > rhcos-live.x86_64.iso
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 to0
. This makes the control plane node schedulable. - 3
- Set the
controlPlane
replicas to1
. In conjunction with the previouscompute
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 the Red Hat OpenShift Cluster Manager. 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.
Generate OpenShift Container Platform assets:
$ mkdir ocp
$ cp install-config.yaml ocp
$ ./openshift-install --dir=ocp create single-node-ignition-config
Embed the ignition data into the RHCOS ISO:
$ alias coreos-installer='podman run --privileged --pull always --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
12.2.3. 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
- On the administration node, insert a USB drive into a USB port.
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.
- On the server, insert the USB drive into a USB port.
- Reboot the server and enter the BIOS settings upon reboot.
- Change boot drive order to make the USB drive boot first.
- Save and exit the BIOS settings. The server will boot with the discovery image.
12.2.4. Monitoring the installation with the Assisted Installer
If you created the ISO using the Assisted Installer, use this procedure to monitor the installation.
Procedure
- 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.
- Click Next until you reach step 3, Networking.
- Select a subnet from the available subnets.
- Keep Use the same host discovery SSH key checked. You can change the SSH public key, if necessary.
- Click Next to proceed to the Review and Create step.
- Click Install cluster.
- 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.
12.2.5. Monitoring the installation manually
If you created the ISO manually, use this procedure to monitor the installation.
Procedure
Monitor the installation:
$ ./openshift-install --dir=ocp wait-for install-complete
The server will restart several times while deploying the control plane.
Optional: After the installation is complete, check the environment:
$ export KUBECONFIG=ocp/auth/kubeconfig
$ oc get nodes
$ oc get clusterversion