In the last blog post Dealing with a Lack of Entropy on your OpenShift Cluster we deployed the rng-tools software as a DaemonSet in a cluster. By using a DaemonSet, we took advantage of the tools that Kubernetes gives us for deploying an application to all targeted nodes in a cluster. This worked well for getting the rng daemon up and running on nodes that required it, but not all software will work this way. What if we need to install or update a package on the host Red Hat CoreOS (RHCOS) boot image? In the past this was always frowned upon/impossible. RHCOS is an immutable OS delivered to you by Red Hat that can not be modified.

Introduction

OpenShift 4 is built upon Red Hat CoreOS (RHCOS), and RHCOS is managed differently than most traditional Operating Systems. Unlike other Kubernetes distributions where you must manage the base Operating System as well as your Kubernetes distribution, with OpenSHift 4 the RHCOS Operating System and the Kubernetes platform are tightly coupled, and management of RHCOS including any system-level configurations is managed by MachineConfigs, and MachineConfigPools. These constructs allow you to manage system configuration and detect configuration drift on your Control Plane and Worker nodes.