add tagsuffix to take image tag suffix (#4364)

* add tagsuffix to take image tag suffix

* add comments to warn about specifications

* add test and error handle

* fix indent

* update comment

* fix merge errors and return updates

* update image update and fix example

* fix yamls formats

remove tabs in yamls

fix space in image name

tag error in name

* fix spacing issue

format of yaml

set example as above

* spacing of spec in testing templates

* change to switch case

api/filters/imagetag/imagetag_test.go

@@ -840,6 +840,45 @@ spec:
 				},
 			},
 		},
+		"updateimagesuffix": {
+			input: `
+group: apps
+apiVersion: v1
+kind: Deployment
+metadata:
+  name: deploysuffix
+spec:
+  template:
+    spec:
+      containers:
+      - image: redis:6.2.6
+        name: redis
+`,
+			expectedOutput: `
+group: apps
+apiVersion: v1
+kind: Deployment
+metadata:
+  name: deploysuffix
+spec:
+  template:
+    spec:
+      containers:
+      - image: redis:6.2.6-alpine
+        name: redis
+`,
+			filter: Filter{
+				ImageTag: types.Image{
+					Name:      "redis",
+					TagSuffix: "-alpine",
+				},
+			},
+			fsSlice: []types.FieldSpec{
+				{
+					Path: "spec/template/spec/containers[]/image",
+				},
+			},
+		},
 	}
 
 	for tn, tc := range testCases {

api/filters/imagetag/updater.go

@@ -5,6 +5,7 @@ package imagetag
 
 import (
 	"sigs.k8s.io/kustomize/api/filters/filtersutil"
+
 	"sigs.k8s.io/kustomize/api/image"
 	"sigs.k8s.io/kustomize/api/types"
 	"sigs.k8s.io/kustomize/kyaml/yaml"
@@ -46,6 +47,9 @@ func (u imageTagUpdater) SetImageValue(rn *yaml.RNode) error {
 	case u.ImageTag.Digest != "":
 		tag = ""
 		digest = u.ImageTag.Digest
+	case u.ImageTag.TagSuffix != "":
+		tag += u.ImageTag.TagSuffix
+		digest = ""
 	}
 
 	// build final image name