Topology controller should avoid template rotation in case of changes to template metadata only

[fabriziopandini]

User Story

As a developer/user/operator I would like to avoid unnecessary machine rollout when using ClusterClass

Detailed Description

As of today the Topology controller automatically triggers a template rotation whenever there is a changes in templates, and this triggers a machine rollout.

This issue is about discussing the option to not trigger template rotation when the changes in template affects only template metadata. In this case, the Topology controller could patch templates in place

Please note that managed topologies are more sensible to this problem due to the cloned from annotations we are adding to each template. By implementing this change, we are reducing the occurrence of machine rollouts to only when it is really necessary (changes to template spec), thus allowing less invasive changes to clusterclass, rebase or eventually in future also transitioning clusters from unmanaged to managed.

Anything else you would like to add:

This is possible under the aussumption that top level metadata from infrastructure/bootstrap templates are not propagated to machines, which is something being discussed in #5397
@sbueringer to confirm

/kind feature
/area topology

[fabriziopandini]

/milestone v1.0
/assign

[sbueringer]

@fabriziopandini As far as I know that the top level metadata of templates is not propagated (only MD.annotations (link)). The code doesn't look like it would propagate it.

But I don't think I tested that case explicitly.

Just to confirm, this issue is about top level template metadata, right?

[fabriziopandini]

Just to confirm, this issue is about top level template metadata, right?

yes