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Understanding an image-based installation and deployment for single-node OpenShift clusters

Image-based installations streamline the deployment process for single-node OpenShift clusters by significantly reducing installation and deployment times.

This approach enables the preinstallation of configured and validated instances of single-node OpenShift on target hosts. These preinstalled hosts can be rapidly reconfigured and deployed at the far edge of the network, including in disconnected environments, with minimal intervention.

Overview of image-based installation and deployment for single-node OpenShift clusters

Deploying infrastructure at the far edge of the network presents challenges for service providers with low bandwidth, high latency, and disconnected environments.

It is also costly and time-consuming to install and deploy single-node OpenShift clusters.

An image-based approach to installing and deploying single-node OpenShift clusters at the far edge of the network overcomes these challenges by separating the installation and deployment stages.

Imaged-based installation

Preinstall multiple hosts with single-node OpenShift at a central site, such as a service depot or a factory. Then, validate the base configuration for these hosts and leverage the image-based approach to perform reproducible factory installs at scale by using a single container image.

Image-based deployment

Ship the preinstalled and validated hosts to a remote site and rapidly reconfigure and deploy the clusters in a matter of minutes by using a configuration image.

Image-based installation for single-node OpenShift clusters

Using the Lifecycle Agent, you can generate an OCI container image that encapsulates an instance of a single-node OpenShift cluster. This image is derived from a dedicated cluster that you can configure with the target OpenShift Container Platform version.

You can reference this image in a live installation ISO to consistently preinstall configured and validated instances of single-node OpenShift to multiple hosts. This approach enables the preparation of hosts at a central location, for example in a factory or service depot, before shipping the preinstalled hosts to a remote site for rapid reconfiguration and deployment.

The following is a high-level overview of the image-based installation process:

  • Generate an image from a single-node OpenShift cluster.

  • Use the OpenShift Container Platform installation program to embed the seed image URL, and other installation artifacts, in a live installation ISO.

  • Start the host using the live installation ISO to preinstall the host.

    During this process, the OpenShift Container Platform installation program installs Red Hat Enterprise Linux CoreOS (RHCOS) to the disk, pulls the image you generated, and precaches release container images to the disk.

  • When the installation completes, the host is ready to ship to the remote site for rapid reconfiguration and deployment.

Image-based deployment for single-node OpenShift clusters

You can use the OpenShift Container Platform installation program to configure and deploy a host that you preinstalled with an image-based installation. To configure the target host with site-specific details, you must create the following resources:

  • The install-config.yaml installation manifest

  • The image-based-config.yaml manifest

The openshift-install program uses these resources to generate a configuration ISO that you attach to the preinstalled target host to complete the deployment.

Image-based installation and deployment components

The following content describes the components in an image-based installation and deployment.

Seed image

OCI container image generated from a dedicated cluster with the target OpenShift Container Platform version.

Seed cluster

Dedicated single-node OpenShift cluster that you use to create a seed image and is deployed with the target OpenShift Container Platform version.

Lifecycle Agent

Generates the seed image, embeds the seed image URL in the live installation ISO, and reconfigures the host during remote site deployment.

openshift-install installation program

Use the openshift-install program to manually create a configuration ISO. Attach the configuration ISO to a preinstalled host to complete the deployment.

Cluster guidelines for an image-based installation and deployment

For a successful image-based installation and deployment, see the following guidelines.

Cluster guidelines

  • If you are using Red Hat Advanced Cluster Management (RHACM), to avoid including any RHACM resources in your seed image, you need to disable all optional RHACM add-ons before generating the seed image.

Seed cluster guidelines

  • If your cluster deployment at the edge of the network requires a proxy configuration, you must create a seed image from a seed cluster featuring a proxy configuration. The proxy configurations do not have to match.

  • If you set a maximum transmission unit (MTU) in the seed cluster, you must set the same MTU value in the static network configuration for the image-based configuration ISO.

  • Your single-node OpenShift seed cluster must have a shared var/lib/containers directory for precaching images during an image-based installation. For more information see the section Configuring a shared container directory between ostree stateroots.

  • Create a seed image from a single-node OpenShift cluster that uses the same hardware as your target bare-metal host. The seed cluster must reflect your target cluster configuration for the following items:

    • CPU topology

      • Number of CPU cores

      • Tuned performance configuration, such as number of reserved CPUs

    • IP version

      Dual-stack networking is not supported in this release.

    • Disconnected registry

      If the target cluster uses a disconnected registry, your seed cluster must use a disconnected registry. The registries do not have to be the same. "

    • FIPS configuration

Software prerequisites for an image-based installation and deployment

An image-based installation and deployment requires the following minimum software versions for these required components.

Table 1. Minimum software requirements
Component Software version

Managed cluster version

4.17

Hub cluster version

4.16

Red Hat Advanced Cluster Management (RHACM)

2.12

Lifecycle Agent

4.16 or later

OpenShift Container Platform installation program

4.17