WIP: Native client apply support

[Danil-Grigorev]

Motivation

Add support for resource apply using unstable-client implementation.

This implementation addresses the need for https://pkg.go.dev/k8s.io/client-go/applyconfigurations, where the need for a custom DSL is justified by limitations of default values for the go structures.

It seems with exception of some resources where API is not designed to use SSA patch, and a separate patch definition needed, this abstraction can simplify usage of the SSA in general cases.

Equivalent structs in rust allow to distinguish a nil value from an ”” (empty string), as a pointer value is wrapped in Option<V>, thus rendering current state of structures sufficient to address limitation in native to object SSA patch usage.

None -> nil
Some(“”) -> “”
Some(“other”) -> “other”

However there is a second problem with TypeMeta. When constructing an object from a type, like &Pod::default(), the structure does not contain type meta from the beginning, although generated or k8s-openapi definitions have all the necessary information for constructing the field.

R::kind() -> kind
R::api_version() -> apiVersion

Solution

Provide a native to the client .apply and .apply_status methods. These can be used to pass a subset of resource changes to be applied via SSA patch.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 26 lines in your changes missing coverage. Please review.

Project coverage is 75.0%. Comparing base (95cf702) to head (770b954).

Files with missing lines	Patch %	Lines
kube-client/src/client/client_ext.rs	0.0%	20 Missing ⚠️
kube-core/src/metadata.rs	0.0%	6 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #1574     +/-   ##
=======================================
- Coverage   75.2%   75.0%   -0.2%     
=======================================
  Files         82      82             
  Lines       7335    7355     +20     
=======================================
  Hits        5514    5514             
- Misses      1821    1841     +20     

Files with missing lines	Coverage Δ
kube-core/src/metadata.rs	67.7% <0.0%> (ø)
kube-client/src/client/client_ext.rs	73.6% <0.0%> (-10.8%)	⬇️

[clux]

interesting idea with the enum here. i am a little skeptical of it's benefit because it means the documentation must be smashed together for all the variants. separated is fairly easy to read on the client side, and doesn't require a new enum (that i'm pretty sure they'd only need to create for this call anyway).

the original style in api:

• client.patch
• client.patch_status
• client.patch_scale
• client.patch_subresource

feels preferable to me, unless you have any good reasons.

[clux]

This name assumption actually severely constrains the usability of patch to only Patch::Apply and the subset of others that happen to be typed to contain the complete metadata.

I.e. it generally excludes merge patches, strategic merge patches and json patches

[Danil-Grigorev]

My idea/end goal here is to simplify some of the pain points, occurring while using Apply patch, without introducing a custom DSL, like in https://pkg.go.dev/k8s.io/client-go/applyconfigurations, just to provide a apiVersion and kind for the apply patch.

It makes sense to address this incompatibility with other patch types. Need to think it through