Chapter 2. Understanding the OpenShift Update Service
For clusters with internet accessibility, Red Hat provides over-the-air updates through an OpenShift Container Platform update service as a hosted service located behind public APIs.
If you are on a restricted network where disconnected clusters cannot access the public APIs, you can install the OpenShift Update Service locally. See Installing and configuring the OpenShift Update Service.
2.1. About the OpenShift Update Service
The OpenShift Update Service (OSUS) provides over-the-air updates to OpenShift Container Platform, including Red Hat Enterprise Linux CoreOS (RHCOS). It provides a graph, or diagram, that contains the vertices of component Operators and the edges that connect them. The edges in the graph show which versions you can safely update to. The vertices are update payloads that specify the intended state of the managed cluster components.
The Cluster Version Operator (CVO) in your cluster checks with the OpenShift Update Service to see the valid updates and update paths based on current component versions and information in the graph. When you request an update, the CVO uses the release image for that update to update your cluster. The release artifacts are hosted in Quay as container images.
To allow the OpenShift Update Service to provide only compatible updates, a release verification pipeline drives automation. Each release artifact is verified for compatibility with supported cloud platforms and system architectures, as well as other component packages. After the pipeline confirms the suitability of a release, the OpenShift Update Service notifies you that it is available.
The OpenShift Update Service displays all recommended updates for your current cluster. If an upgrade path is not recommended by the OpenShift Update Service, it might be because of a known issue with the update or the target release.
Two controllers run during continuous update mode. The first controller continuously updates the payload manifests, applies the manifests to the cluster, and outputs the controlled rollout status of the Operators to indicate whether they are available, upgrading, or failed. The second controller polls the OpenShift Update Service to determine if updates are available.
Only upgrading to a newer version is supported. Reverting or rolling back your cluster to a previous version is not supported. If your update fails, contact Red Hat support.
During the update process, the Machine Config Operator (MCO) applies the new configuration to your cluster machines. The MCO cordons the number of nodes as specified by the maxUnavailable field on the machine configuration pool and marks them as unavailable. By default, this value is set to 1. The MCO then applies the new configuration and reboots the machine.
If you use Red Hat Enterprise Linux (RHEL) machines as workers, the MCO does not update the kubelet because you must update the OpenShift API on the machines first.
With the specification for the new version applied to the old kubelet, the RHEL machine cannot return to the Ready state. You cannot complete the update until the machines are available. However, the maximum number of unavailable nodes is set to ensure that normal cluster operations can continue with that number of machines out of service.
The OpenShift Update Service is composed of an Operator and one or more application instances.
2.2. Support policy for unmanaged Operators
The management state of an Operator determines whether an Operator is actively managing the resources for its related component in the cluster as designed. If an Operator is set to an unmanaged state, it does not respond to changes in configuration nor does it receive updates.
While this can be helpful in non-production clusters or during debugging, Operators in an unmanaged state are unsupported and the cluster administrator assumes full control of the individual component configurations and upgrades.
An Operator can be set to an unmanaged state using the following methods:
Individual Operator configuration
Individual Operators have a
managementStateparameter in their configuration. This can be accessed in different ways, depending on the Operator. For example, the Cluster Logging Operator accomplishes this by modifying a custom resource (CR) that it manages, while the Cluster Samples Operator uses a cluster-wide configuration resource.Changing the
managementStateparameter toUnmanagedmeans that the Operator is not actively managing its resources and will take no action related to the related component. Some Operators might not support this management state as it might damage the cluster and require manual recovery.WarningChanging individual Operators to the
Unmanagedstate renders that particular component and functionality unsupported. Reported issues must be reproduced inManagedstate for support to proceed.Cluster Version Operator (CVO) overrides
The
spec.overridesparameter can be added to the CVO’s configuration to allow administrators to provide a list of overrides to the CVO’s behavior for a component. Setting thespec.overrides[].unmanagedparameter totruefor a component blocks cluster upgrades and alerts the administrator after a CVO override has been set:Disabling ownership via cluster version overrides prevents upgrades. Please remove overrides before continuing.
WarningSetting a CVO override puts the entire cluster in an unsupported state. Reported issues must be reproduced after removing any overrides for support to proceed.
