Red Hat Summit1장. Machine configuration overview
There are times when you need to make changes to the operating systems running on OpenShift Container Platform nodes. This can include changing settings for network time service, adding kernel arguments, or configuring journaling in a specific way.
Aside from a few specialized features, most changes to operating systems on OpenShift Container Platform nodes can be done by creating what are referred to as MachineConfig objects that are managed by the Machine Config Operator. For example, you can use the Machine Config Operator (MCO) and machine configs to manage update to systemd, CRI-O and kubelet, the kernel, Network Manager and other system features.
Tasks in this section describe how to use features of the Machine Config Operator to configure operating system features on OpenShift Container Platform nodes.
NetworkManager stores new network configurations to /etc/NetworkManager/system-connections/ in a key file format.
Previously, NetworkManager stored new network configurations to /etc/sysconfig/network-scripts/ in the ifcfg format. Starting with RHEL 9.0, RHEL stores new network configurations at /etc/NetworkManager/system-connections/ in a key file format. The connections configurations stored to /etc/sysconfig/network-scripts/ in the old format still work uninterrupted. Modifications in existing profiles continue updating the older files.
1.1. About the Machine Config Operator
OpenShift Container Platform 4.21 integrates both operating system and cluster management. Because the cluster manages its own updates, including updates to Red Hat Enterprise Linux CoreOS (RHCOS) on cluster nodes, OpenShift Container Platform provides an opinionated lifecycle management experience that simplifies the orchestration of node upgrades.
OpenShift Container Platform employs three daemon sets and controllers to simplify node management. These daemon sets orchestrate operating system updates and configuration changes to the hosts by using standard Kubernetes-style constructs. They include:
-
The
machine-config-controller, which coordinates machine upgrades from the control plane. It monitors all of the cluster nodes and orchestrates their configuration updates. -
The
machine-config-daemondaemon set, which runs on each node in the cluster and updates a machine to configuration as defined by machine config and as instructed by the MachineConfigController. When the node detects a change, it drains off its pods, applies the update, and reboots. These changes come in the form of Ignition configuration files that apply the specified machine configuration and control kubelet configuration. The update itself is delivered in a container. This process is key to the success of managing OpenShift Container Platform and RHCOS updates together. -
The
machine-config-serverdaemon set, which provides the Ignition config files to control plane nodes as they join the cluster.
The machine configuration is a subset of the Ignition configuration. The machine-config-daemon reads the machine configuration to see if it needs to do an OSTree update or if it must apply a series of systemd kubelet file changes, configuration changes, or other changes to the operating system or OpenShift Container Platform configuration.
When you perform node management operations, you create or modify a KubeletConfig custom resource (CR).
When changes are made to a machine configuration, the Machine Config Operator (MCO) automatically reboots all corresponding nodes in order for the changes to take effect.
You can mitigate the disruption caused by some machine config changes by using a node disruption policy. See Understanding node restart behaviors after machine config changes.
Alternatively, you can prevent the nodes from automatically rebooting after machine configuration changes before making the changes. Pause the autoreboot process by setting the spec.paused field to true in the corresponding machine config pool. When paused, machine configuration changes are not applied until you set the spec.paused field to false and the nodes have rebooted into the new configuration.
When the MCO detects any of the following changes, it applies the update without draining or rebooting the node:
-
Changes to the SSH key in the
spec.config.passwd.users.sshAuthorizedKeysparameter of a machine config. -
Changes to the global pull secret or pull secret in the
openshift-confignamespace. -
Automatic rotation of the
/etc/kubernetes/kubelet-ca.crtcertificate authority (CA) by the Kubernetes API Server Operator.
-
Changes to the SSH key in the
When the MCO detects changes to the
/etc/containers/registries.conffile, such as editing anImageDigestMirrorSet,ImageTagMirrorSet, orImageContentSourcePolicyobject, it drains the corresponding nodes, applies the changes, and uncordons the nodes. The node drain does not happen for the following changes:-
The addition of a registry with the
pull-from-mirror = "digest-only"parameter set for each mirror. -
The addition of a mirror with the
pull-from-mirror = "digest-only"parameter set in a registry. -
The addition of items to the
unqualified-search-registrieslist.
-
The addition of a registry with the
There might be situations where the configuration on a node does not fully match what the currently-applied machine config specifies. This state is called configuration drift. The Machine Config Daemon (MCD) regularly checks the nodes for configuration drift. If the MCD detects configuration drift, the MCO marks the node degraded until an administrator corrects the node configuration. A degraded node is online and operational, but, it cannot be updated.
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