Update child cluster infrastructure

Prior to MKE 4.2.1 it was necessary recreate a child cluster to change its infrastructure. Starting with MKE 4.2.1, though, MKE 4 supports infrastructure updates for existing AWS and vSphere child clusters. This includes such changes as resizing instances/VMs, updating disk sizes, changing the machine image/template, and rotating vSphere connection settings.

How infrastructure updates are made

To make a change to the infrastructure of a child cluster, you update the infrastructure configuration for the cluster and then reapply it. Under the hood, MKE renders the updated infrastructure into the cluster CAPI MachineTemplate. As MachineTemplates are immutable, any infrastructure changea result in a new template and a subsequent rolling replacement of the affected machines by CAPI, be it the control plane, workers, or both, depending on what has been changed.

How infrastructure updates are applied

Each provider derives its MachineTemplate name from a content hash of a specific subset of infrastructure fields. Editing a field in that subset renames the template, which causes CAPI to roll the affected machines, draining and replacing them one at a time. Editing a field outside that subset leaves the template name unchanged, so no rolling replacement occurs.

The control-plane template and the worker template hash different, but overlapping, subsets of fields. As a result, a given edit may roll the control plane only, the workers only, or both, depending on which subset the edited field belongs to.

infrastructure change rollout matrices

AWS

Field	Rollout scope
infrastructure.controlPlane instanceType rootVolumeSize amiID imageLookup iamInstanceProfile nonRootVolumes uncompressedUserData	Control plane
infrastructure.worker instanceType rootVolumeSize amiID imageLookup iamInstanceProfile nonRootVolumes uncompressedUserData	Workers
infrastructure.publicIP	Both (control plane and workers)
infrastructure.region infrastructure.sshKeyName infrastructure.bastion clusterIdentity (top-level, outside infrastructure)	No rolling replacement as these are not part of the template hash (cluster-wide settings; some may be immutable or have no effect on an existing cluster).

vSphere

Field	Rollout scope
infrastructure.controlPlane cpus memory rootVolumeSize vmTemplate network	Control plane
infrastructure.worker cpus memory rootVolumeSize vmTemplate network	Workers
infrastructure.vsphere server thumbprint datacenter datastore resourcePool folder	Both (control plane and workers)
infrastructure.nameservers	Both (control plane and workers)
infrastructure.ipamEnabled	Both (control plane and workers)
infrastructure.ipPool	Both (control plane and workers)
infrastructure.controlPlaneEndpointIP	Immutable after creation. MKE rejects changes to this field on an existing child cluster.