Merge pull request #41268 from sagidlow/OSDOCS-3068

OSDOCS-3068: Adding an intro to Updates docs

Author: sagidlow

_topic_maps/_topic_map.yml

@@ -430,6 +430,8 @@ Name: Updating clusters
 Dir: updating
 Distros: openshift-origin,openshift-enterprise
 Topics:
+- Name: Understanding OpenShift updates
+  File: understanding-openshift-updates
 - Name: Understanding the OpenShift Update Service
   File: understanding-the-update-service
 - Name: Installing and configuring the OpenShift Update Service

modules/update-common-terms.adoc

@@ -0,0 +1,29 @@
+// Module included in the following assemblies:
+//
+// * updating/understanding-openshift-updates.adoc
+
+:_content-type: REFERENCE
+[id="update-common-terms_{context}"]
+= Common terms
+
+Control plane:: The _control plane_, which is composed of control plane machines, manages the {product-title} cluster. The control plane machines manage workloads on the compute machines, which are also known as worker machines.
+
+Cluster Version Operator:: The _Cluster Version Operator_ (CVO) starts the update process for the cluster. It checks with OSUS based on the current cluster version and retrieves the graph which contains available or possible update paths.
+
+Machine Config Operator:: The _Machine Config Operator_ (MCO) is a cluster-level Operator that manages the operating system and machine configurations. Through the MCO, platform administrators can configure and update systemd, CRI-O and Kubelet, the kernel, NetworkManager, and other system features on the worker nodes.
++
+For more information, see link:https://docs.openshift.com/container-platform/latest/post_installation_configuration/machine-configuration-tasks.html#machine-config-overview-post-install-machine-configuration-tasks[Machine config overview].
+
+OpenShift Update Service:: The _OpenShift Update Service_ (OSUS) provides over-the-air updates to {product-title}, including to {op-system-first}. It provides a graph, or diagram, that contains the vertices of component Operators and the edges that connect them.
++
+For more information, see link:https://docs.openshift.com/container-platform/latest/updating/understanding-the-update-service.html#update-service-overview_understanding-the-update-service[About the OpenShift Update Service].
+
+Channels:: _Channels_ declare an update strategy tied to minor versions of {product-title}. The OSUS uses this configured strategy to recommend update edges consistent with that strategy.
++
+For more information, see link:https://docs.openshift.com/container-platform/latest/updating/understanding-upgrade-channels-release.html[Understanding update channels and releases].
+
+Recommended update edge:: A _recommended update edge_ is a recommended update between {product-title} releases.  Whether a given update is recommended can depend on the cluster's configured channel, current version, known bugs, and other information. OSUS communicates the recommended edges to the CVO, which runs in every cluster.
+
+Extended Update Support:: All post-4.7 even-numbered minor releases are labeled as _Extended Update Support_ (EUS) releases. These releases introduce a verified update path between EUS releases, permitting customers to streamline updates of worker worker nodes and formulate update strategies of EUS-to-EUS {product-title} releases that will cause fewer reboots of worker nodes.
++
+For more information, see link:https://access.redhat.com/support/policy/updates/openshift-eus[Red Hat OpenShift Extended Update Support (EUS) Overview].

updating/understanding-openshift-updates.adoc

@@ -0,0 +1,15 @@
+:_content-type: ASSEMBLY
+[id="understanding-openshift-updates"]
+= Understanding {product-title} updates
+include::modules/common-attributes.adoc[]
+:context: understanding-openshift-updates
+
+toc::[]
+
+With {product-title} 4, you can update a {product-title} cluster with a single operation by using the web console or the OpenShift CLI (`oc`). Platform administrators are automatically notified when an update is available for their cluster.
+
+The OpenShift Update Service (OSUS) builds a graph of upgrade possibilities based on release images in the registry.
+The graph is based on recommended, tested update paths from a specific version. {product-title} clusters connect to the Red Hat Hybrid Cloud servers and identify which clusters the user is running, along with the version information. OSUS responds with information about known update targets. Either a cluster administrator or an automatic update controller edits the custom resource (CR) of the Cluster Version Operator (CVO) with the new version to update to.
+After the CVO receives the update image from the registry, the CVO then applies the changes.
+
+include::modules/update-common-terms.adoc[leveloffset=+1]