Redhat OpenShift – Notes for Beginner

Openshift is a container hosting platform that provides options to deploy containers with smart orchestration options.

Various issue addressed by Openshift/Kubernetes – Problems Addressed

Installation
- 4 Ways to deploy the cluster
  - Interactive – web-based Assisted Installer.
  - Local Agent Based – deploy a cluster locally with the Agent-based Installer for disconnected environments or restricted networks. you must download and configure the Agent-based Installer first. Configuration is done with a command-line interface. This approach is ideal for disconnected environments.
  - Automated – The installation program uses each cluster host’s baseboard management controller (BMC) for provisioning. You can deploy clusters in connected or disconnected environments.
  - Full Control – deploy a cluster on infrastructure that you prepare and maintain, which provides maximum customizability. You can deploy clusters in connected or disconnected environments.
The installation program generates the main assets, such as
- Ignition config files for the bootstrap
- control plane, and
- compute machines.
- You can start an OpenShift Container Platform cluster with these three machine configurations, provided you correctly configured the infrastructure.
Installation Targets and dependencies –

Post-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. RHCOS 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 4.18 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 a bootable container image, using OSTree as a backend, that is deployed across the cluster by the Machine Config Operator. Actual operating system changes are made in-place on each machine as an atomic operation by using rpm-ostree.