modifying annotation and label using KRM function

main.go

package main

import (
	"bytes"
	"log"
	"os"

	"sigs.k8s.io/kustomize/kyaml/kio"
	"sigs.k8s.io/kustomize/kyaml/yaml"
)

func main() {
	input := bytes.NewReader([]byte(`apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.7.9
        ports:
        - containerPort: 80
---
apiVersion: v1
kind: Service
metadata:
  name: nginx
spec:
  selector:
    app: nginx
  ports:
    - protocol: TCP
      port: 80
      targetPort: 80
`))
	// setAnnotationFn
	setAnnotationFn := kio.FilterFunc(func(operand []*yaml.RNode) ([]*yaml.RNode, error) {
		for i := range operand {
			resource := operand[i]
			_, err := resource.Pipe(yaml.SetAnnotation("foo", "bar"))
			resource.Pipe(yaml.SetK8sNamespace("testinghamza"))
			if err != nil {
				return nil, err
			}
		}
		return operand, nil
	})

	setLabelFn := kio.FilterFunc(func(operand []*yaml.RNode) ([]*yaml.RNode, error) {
		for i := range operand {
			resource := operand[i]
			_, err := resource.Pipe(yaml.SetLabel("hi", "how are you"))
			if err != nil {
				return nil, err
			}
		}
		return operand, nil
	})

	err := kio.Pipeline{
		Inputs:  []kio.Reader{&kio.ByteReader{Reader: input}},
		Filters: []kio.Filter{setAnnotationFn, setLabelFn},
		Outputs: []kio.Writer{kio.ByteWriter{Writer: os.Stdout}},
	}.Execute()
	if err != nil {
		log.Fatal(err)
	}
}