The OpenShift Container Platform installation program offers you flexibility. You can use the installation program to deploy a cluster on infrastructure that the installation program provisions and the cluster maintains or deploy a cluster on infrastructure that you prepare and maintain.
These two basic types of OpenShift Container Platform clusters are frequently called installer-provisioned infrastructure clusters and user-provisioned infrastructure clusters.
Both types of clusters have the following characteristics:
Highly available infrastructure with no single points of failure is available by default
Administrators maintain control over what updates are applied and when
You use the same installation program to deploy both types of clusters. The main assets generated by the installation program are the Ignition config files for the bootstrap, master, and worker machines. With these three configurations and correctly configured infrastructure, you can start an OpenShift Container Platform cluster.
The OpenShift Container Platform installation program uses a set of targets and dependencies to manage cluster installation. The installation program has a set of targets that it must achieve, and each target has a set of dependencies. Because each target is only concerned with its own dependencies, the installation program can act to achieve multiple targets in parallel. The ultimate target is a running cluster. By meeting dependencies instead of running commands, the installation program is able to recognize and use existing components instead of running the commands to create them again.
The following diagram shows a subset of the installation targets and dependencies:
After installation, each cluster machine uses Red Hat Enterprise Linux CoreOS (RHCOS) as the operating system. RHCOS is the immutable container host version of Red Hat Enterprise Linux (RHEL) and features a RHEL kernel with SELinux enabled by default. It includes the
kubelet, which is the Kubernetes node agent, and the CRI-O container runtime, which is optimized for Kubernetes.
Every control plane machine in an OpenShift Container Platform 4.8 cluster must use RHCOS, which includes a critical first-boot provisioning tool called Ignition. This tool enables the cluster to configure the machines. Operating system updates are delivered as an Atomic OSTree repository that is embedded in a container image that is rolled out across the cluster by an Operator. Actual operating system changes are made in-place on each machine as an atomic operation by using rpm-ostree. Together, these technologies enable OpenShift Container Platform to manage the operating system like it manages any other application on the cluster, via in-place upgrades that keep the entire platform up-to-date. These in-place updates can reduce the burden on operations teams.
If you use RHCOS as the operating system for all cluster machines, the cluster manages all aspects of its components and machines, including the operating system. Because of this, only the installation program and the Machine Config Operator can change machines. The installation program uses Ignition config files to set the exact state of each machine, and the Machine Config Operator completes more changes to the machines, such as the application of new certificates or keys, after installation.
In OpenShift Container Platform 4.8, you can install a cluster that uses installer-provisioned infrastructure on the following platforms:
Amazon Web Services (AWS)
Google Cloud Platform (GCP)
Red Hat OpenStack Platform (RHOSP) version 13 and 16
The latest OpenShift Container Platform release supports both the latest RHOSP long-life release and intermediate release. For complete RHOSP release compatibility, see the OpenShift Container Platform on RHOSP support matrix.
Red Hat Virtualization (RHV)
VMware Cloud (VMC) on AWS
For these clusters, all machines, including the computer that you run the installation process on, must have direct internet access to pull images for platform containers and provide telemetry data to Red Hat.
After installation, the following changes are not supported:
In OpenShift Container Platform 4.8, you can install a cluster that uses user-provisioned infrastructure on the following platforms:
VMware Cloud on AWS
IBM Z or LinuxONE
IBM Power Systems
Depending on the supported cases for the platform, installations on user-provisioned infrastructure allow you to run machines with full internet access, place your cluster behind a proxy, or perform a restricted network installation. In a restricted network installation, you can download the images that are required to install a cluster, place them in a mirror registry, and use that data to install your cluster. While you require internet access to pull images for platform containers, with a restricted network installation on vSphere or bare metal infrastructure, your cluster machines do not require direct internet access.
The OpenShift Container Platform 4.x Tested Integrations page contains details about integration testing for different platforms.
When you install an OpenShift Container Platform cluster, you download the installation program from the appropriate Infrastructure Provider page on the OpenShift Cluster Manager site. This site manages:
REST API for accounts
Registry tokens, which are the pull secrets that you use to obtain the required components
Cluster registration, which associates the cluster identity to your Red Hat account to facilitate the gathering of usage metrics
In OpenShift Container Platform 4.8, the installation program is a Go binary file that performs a series of file transformations on a set of assets. The way you interact with the installation program differs depending on your installation type.
For clusters with installer-provisioned infrastructure, you delegate the infrastructure bootstrapping and provisioning to the installation program instead of doing it yourself. The installation program creates all of the networking, machines, and operating systems that are required to support the cluster.
If you provision and manage the infrastructure for your cluster, you must provide all of the cluster infrastructure and resources, including the bootstrap machine, networking, load balancing, storage, and individual cluster machines.
You use three sets of files during installation: an installation configuration file that is named
install-config.yaml, Kubernetes manifests, and Ignition config files for your machine types.
It is possible to modify Kubernetes and the Ignition config files that control the underlying RHCOS operating system during installation. However, no validation is available to confirm the suitability of any modifications that you make to these objects. If you modify these objects, you might render your cluster non-functional. Because of this risk, modifying Kubernetes and Ignition config files is not supported unless you are following documented procedures or are instructed to do so by Red Hat support.