yamlpath

Example uses a Path to find certain nodes and replace their content. Unlike a global change, it avoids false positives.

y := `---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: sample-deployment
spec:
  template:
    spec:
      containers:
      - name: nginx
        image: nginx
        ports:
        - containerPort: 80
      - name: nginy
        image: nginy
        ports:
        - containerPort: 81
`
var n yaml.Node

err := yaml.Unmarshal([]byte(y), &n)
if err != nil {
	log.Fatalf("cannot unmarshal data: %v", err)
}

p, err := yamlpath.NewPath("$..spec.containers[*].image")
if err != nil {
	log.Fatalf("cannot create path: %v", err)
}

q, err := p.Find(&n)
if err != nil {
	log.Fatalf("unexpected error: %v", err)
}

for _, i := range q {
	i.Value = "example.com/user/" + i.Value
}

var buf bytes.Buffer
e := yaml.NewEncoder(&buf)
defer e.Close()
e.SetIndent(2)

err = e.Encode(&n)
if err != nil {
	log.Printf("Error: cannot marshal node: %v", err)
	return
}

z := `apiVersion: apps/v1
kind: Deployment
metadata:
  name: sample-deployment
spec:
  template:
    spec:
      containers:
      - name: nginx
        image: example.com/user/nginx
        ports:
        - containerPort: 80
      - name: nginy
        image: example.com/user/nginy
        ports:
        - containerPort: 81
`
if buf.String() == z {
	fmt.Printf("success")
} else {
	dmp := diffmatchpatch.New()
	diffs := dmp.DiffMain(buf.String(), z, false)
	fmt.Println(diffs)
}

Output:

success