[Proposal] Add a 'podSpecPath' field in WorkloadDefinition

[wonderflow]

We have discussed a lot and finally conclude to add labels like workload.oam.dev/podspecable to indicate the workload will contain 'podSpec' in it's spec.

But it's hard to know which field is podSpec, so I propose we add a 'podSpecPath' field in WorkloadDefinition.

By defualt, if workload.oam.dev/podspecable: true label is set but podSpecPath not, we may go to spec.template to find 'podTemplate', and get 'podSpec' in spec.template.spec.

If this field is set like below, we will directly regard path specified in podSpecPath as podSpec path, in this example, it's spec.podSpec

apiVersion: core.oam.dev/v1alpha2
kind: WorkloadDefinition
metadata:
  name: webservice
  labels:
     workload.oam.dev/podspecable: true
  annotations:
    definition.oam.dev/apiVersion: "standard.oam.dev/v1alpha1"
    definition.oam.dev/kind: "PodSpecWorkload"
spec:
  podSpecPath: "spec.podSpec"
  definitionRef:
    name: podspecworkloads.standard.oam.dev
  childResourceKinds:
    - apiVersion: apps/v1
      kind: Deployment
    - apiVersion: v1
      kind: Service

This is also needed to fix kubevela/kubevela#354

[resouer]

+1, I also noticed this issue for a while: podspecable doesn't mean spec.template.spec exists.

[hongchaodeng]

+1.
Shouldn't it be podSpecFieldPath ?

[ryanzhang-oss]

This reminds me of the workloadRefPath which caused some problems when it is not presented (#232). I know this will be an optional field too, I wonder what's the exact behavior when this field is not present?

[resouer]

@ryanzhang-oss This field doesn't need to present if:

1. the workload is not podspecable,
2. the workload is podspecable but assume 'template.spec' as pod spec field path.

A workload is podspecable if the podspecable label present on its definition.

[wonderflow]

@hongchaodeng @resouer podSpecPath is better as we already have workloadRefPath.

@ryanzhang-oss Yes, it's an optional field as I said in the proposal, it could have following behaviors:

No label and No podSpecPath set

apiVersion: core.oam.dev/v1alpha2
kind: WorkloadDefinition
metadata:
  name: webservice
spec:
  definitionRef:
    name: podspecworkloads.standard.oam.dev
   ...

In this case, we will not do any podSpec specific thing.

Has label with No podSpecPath set

apiVersion: core.oam.dev/v1alpha2
kind: WorkloadDefinition
metadata:
  name: webservice
  labels:
     workload.oam.dev/podspecable: true
spec:
  definitionRef:
    name: podspecworkloads.standard.oam.dev
   ...

In this case, we will always regard spec.template.spec as the podSpecPath. This will fit with K8s Deployment/StatefulSet and many other CRD Objects like OpenKruise CloneSet/Knative Service.

Has podSpecPath set

apiVersion: core.oam.dev/v1alpha2
kind: WorkloadDefinition
metadata:
  name: webservice
  labels:
     workload.oam.dev/podspecable: true
spec:
  podSpecPath: "spec.podSpec"
  definitionRef:
    name: podspecworkloads.standard.oam.dev
   ...

In this case, whether there's label or not, we will always make the workload as podspecable=true. We will find podSpecPath to get the field of podSpec.