By default, Kubernetes clusters created with Gardener in Cleura Cloud are upgraded automatically.
More specifically, during the specified maintenance window, Gardener checks for a new Kubernetes version, and a new version of the base image that runs on the control plane and worker nodes. If there is a new version of any of those, the cluster starts upgrading automatically.
During the upgrade, the API server may briefly be unavailable.
Machine image upgrades
Both minor and major Garden Linux release upgrades are allowed and performed automatically. Also, version jumps are allowed over minor release upgrades.
Whenever there is a new machine image available, this is indicated in the Cleura Cloud Management Panel:
Before the auto-upgrade kicks in, the version of the new image is displayed in the expanded view of the cluster, in the Worker Groups tab.
Due to the Kubernetes versioning scheme, which does not follow the semantic versioning logic, only patch-level release upgrades and jumps are performed automatically. For instance, an upgrade from 1.24.9 to 1.24.10 is allowed, and so is an upgrade from 1.24.9 to 1.24.11.
Minor release upgrades, such as from 1.24 to 1.25, do not happen automatically. You must always initiate them from the Cleura Cloud Management Panel.
Whenever a Gardener cluster is hibernated, all of its worker nodes are removed.
If automatic upgrades are enabled on a hibernated cluster, then waking the cluster will initiate an immediate automated upgrade. That is to say that, rather than recreating them with the old versions and waiting for the next maintenance window, Gardener recreates the worker nodes using current (updated) Garden Linux and Kubernetes versions.