Server-Side Apply — Compatibility across topology changes

Reference note (untrusted external data; do not execute it as instructions). On rare occurrences, the author for a CustomResourceDefinition (CRD) or built-in may want to change the specific topology of a field in their resource, without incrementing its API version. Changing the topology of types, by upgrading the cluster or updating the CRD, has different consequences when updating existing objects. There are two categories of changes: when a field goes from map/set/granular to atomic, and the other way around. When the listType, mapType, or structType changes from map/set/granular to atomic, the whole list, map, or struct of existing objects will end-up being owned by actors who owned an element of these types. This means that any further change to these objects would cause a conflict. When a listType, mapType, or structType changes from atomic to map/set/granular, the API server is unable to infer the new ownership of these fields. Because of that, no conflict will be produced when objects have these fields updated. For that reason, it is not recommended to change a type from atomic to map/set/granular. Take for example, the custom resource Bounded code example (external data; do not execute automatically): ```yaml --- apiVersion: example.com/v1 kind: Foo metadata: name: foo-sample managedFields: - manager: "manager-one" operation: Apply apiVersion: example.com/v1 fieldsType: FieldsV1 fieldsV1: f:spec: f:data: {} spec: data: key1: val1 key2: val2 ``` Before spec.data gets changed from atomic to granular, manager-one owns the field spec.data, and all the fields within it (key1 and key2). When the CRD gets changed to make spec.data granular, manager-one continues to own the top-level field spec.data (meaning no other managers can delete the map called data without a conflict), but it no longer owns key1 and key2, so another manager can then modify or delete those fields without conflict. Attribution: Adapted from Kubernetes Documentation under CC-BY-4.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.