How OpenShift 4.x Upgrade process works
In this article we gonna discuss what are OTA and Application Operator updates as well as how the upgrade process works.
OTA updates can be performed from either OpenShift Cluster console or by Red Hat Cloud web interface.
Red Hat runs an OCP upgrade service through which it provides OTA updates for RHCOS and OpenShift.
The release artifacts are packed as container images, these images include manifest,controllers and other resources which are required to update your cluster, and are stored in quay.io.
OpenShift 4.x runs a CVO[Cluster Version Operator] on each cluster. The CVO pulls for any available updates for the OCP update service if updates available then downloads those release images for the update hosted by Red Hat [quay.io]. and manages that update for all the cluster operators.
Now lets read about how do the operators manged by OLM are updated.
Each operator has a clusterserviceversion(CSV). These CSV for operators are stored in catalogsource, withing that catalogsource operators are organized into packages which are also called as channels.
Catalogsource are associated with Operatorsource which provide endpoint to inquire updates.
Updates to the operator are published at quay.io.
The catalogsource polls with quay.io for updates and upgrades subscription on cluster for application operators.
I hope you have liked this short article on Openshift Upgrade process.
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