Metadata-only operations

[olix0r]

I recently noticed that client-go supports operations that only interact with resource metadata via the PartialObjectMetadata type. This can allow controllers to substantially reduce I/O and memory requirements when they don't actually need an object's spec or status.

I haven't found any analogs in the kube-rs ecosystem. Do they exist? If not, do you have any thoughts about where/how this should be implemented?

[clux]

It seems to be available on Kubernetes > 1.14, although it's not listed as verbs in the openapi spec so it's gone under the radar. We should almost certainly add support for this.

The request there sets a header for a protobuf specific request, but if it works outside protobuf, then we could probably expose getters/setters on Api that treat it like other subresources (since that feels pretty similar here):

• async fn get_metadata(name: &str) -> Result<ObjectMeta>
• async fn list_metadata(lp: &ListParams) -> Result<ObjectList<ObjectMeta>> ? not sure if the return type is wrapped in the native list type
• async fn patch_metadata(name: &str, pp: &PatchParams, patch: &Patch<P>) -> Result<ObjectMeta>
• async fn watch_metadata(lp: &ListParams, version: &str) -> Result<impl Stream<Item = Result<WatchEvent<ObjectMeta>>>> maybe? not sure how the final wrap would look like coming out of the api

If it doesn't work outside protobuf, then it's possible we could still introduce these as a first go for protobuf support by sketching out ObjectMeta protobufs correctly first. The types for it would exist in k8s-pb.

WDYT?

[olix0r]

The request there sets a header for a protobuf specific request

True, but note that Accept includes:

• application/vnd.kubernetes.protobuf;as=PartialObjectMetadata;g=meta.k8s.io;v=v1
• application/json;as=PartialObjectMetadata;g=meta.k8s.io;v=v1
• application/json

So, I'm hopeful we should be able to decouple this from protobuf support.

[olix0r]

Tracked in #1027