Why kubernetes services do not support matchExpressions?

General Discussions
1

I already asked this on Stack Overflow:

In Kuberntes,
resources, such as Job, Deployment, ReplicaSet, and DaemonSet, support matchExpressions.
but Service resources do not support matchExpressions in spec.selector.

What I tried:

I tried to create a service with matchExpressions in selector:

vim test-svc.yaml

apiVersion: v1
kind: Service
metadata:
  name: my-service
spec:
  selector:
    matchExpressions:
      - { key: appname, operator: In, values: [myapp, myniceapp, mygreatapp]}
  ports:
  - name: tcp
    port: 8080
    targetPort: 8080
  type: ClusterIP

then

kunectl apply -f test-svc.yaml

and I get error:

error: error validating "test-svc.yaml": error validating data: ValidationError(Service.spec.selector.matchExpressions): invalid type for io.k8s.api.core.v1.ServiceSpec.selector: got "array", expected "string"; if you choose to ignore these errors, turn validation off with --validate=false

What I expected:

I expected to be able to create a service with matchExpressions as selector.
and I’m eager to know what is the reasoning behind this limit.

2

The service API predates “modern” selectors, and because of API compatibility has not yet tried to be updated.

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