Implement replica transformer as patch alternative

pkg/replica/replica.go

@@ -0,0 +1,13 @@
+package replica
+
+// Replica specifies a modification to a replica config.
+// The number of replicas of a resource whose name matches will be set to count.
+// This struct is used by the ReplicaCountTransform, and is meant to supplement
+// the existing patch functionality with a simpler syntax for replica configuration.
+type Replica struct {
+	// The name of the resource to change the replica count
+	Name string `json:"name,omitempty" yaml:"name,omitempty"`
+
+	// The number of replicas required.
+	Count uint `json:"count,omitempty" yaml:"count,omitempty"`
+}

pkg/target/kusttarget_configplugin.go

@@ -7,6 +7,7 @@ import (
 	"github.com/pkg/errors"
 	"sigs.k8s.io/kustomize/pkg/image"
 	"sigs.k8s.io/kustomize/pkg/plugins"
+	"sigs.k8s.io/kustomize/pkg/replica"
 	"sigs.k8s.io/kustomize/pkg/transformers"
 	"sigs.k8s.io/kustomize/pkg/transformers/config"
 	"sigs.k8s.io/kustomize/pkg/types"
@@ -69,6 +70,7 @@ func (kt *KustTarget) configureBuiltinTransformers(
 		kt.configureBuiltinLabelTransformer,
 		kt.configureBuiltinAnnotationsTransformer,
 		kt.configureBuiltinPatchJson6902Transformer,
+		kt.configureBuiltinReplicaCountTransformer,
 	}
 	var result []transformers.Transformer
 	for _, f := range configurators {
@@ -233,6 +235,26 @@ func (kt *KustTarget) configureBuiltinImageTagTransformer(
 	return
 }
 
+func (kt *KustTarget) configureBuiltinReplicaCountTransformer(
+	tConfig *config.TransformerConfig) (
+	result []transformers.Transformer, err error) {
+	var c struct {
+		Replica    replica.Replica
+		FieldSpecs []config.FieldSpec
+	}
+	for _, args := range kt.kustomization.Replicas {
+		c.Replica = args
+		c.FieldSpecs = tConfig.Replicas
+		p := builtin.NewReplicaCountTransformerPlugin()
+		err = kt.configureBuiltinPlugin(p, c, "replica")
+		if err != nil {
+			return nil, err
+		}
+		result = append(result, p)
+	}
+	return
+}
+
 func (kt *KustTarget) configureBuiltinPlugin(
 	p plugins.Configurable, c interface{}, id string) (err error) {
 	var y []byte

pkg/transformers/config/transformerconfig.go

@@ -35,6 +35,7 @@ type TransformerConfig struct {
 	NameReference     nbrSlice `json:"nameReference,omitempty" yaml:"nameReference,omitempty"`
 	VarReference      fsSlice  `json:"varReference,omitempty" yaml:"varReference,omitempty"`
 	Images            fsSlice  `json:"images,omitempty" yaml:"images,omitempty"`
+	Replicas          fsSlice  `json:"replicas,omitempty" yaml:"replicas,omitempty"`
 }
 
 // MakeEmptyConfig returns an empty TransformerConfig object
@@ -61,6 +62,7 @@ func (t *TransformerConfig) sortFields() {
 	sort.Sort(t.NameReference)
 	sort.Sort(t.VarReference)
 	sort.Sort(t.Images)
+	sort.Sort(t.Replicas)
 }
 
 // AddPrefixFieldSpec adds a FieldSpec to NamePrefix

pkg/types/kustomization.go

@@ -22,6 +22,7 @@ import (
 
 	"sigs.k8s.io/kustomize/pkg/gvk"
 	"sigs.k8s.io/kustomize/pkg/image"
+	"sigs.k8s.io/kustomize/pkg/replica"
 )
 
 const (
@@ -79,6 +80,10 @@ type Kustomization struct {
 	// patch, but this operator is simpler to specify.
 	Images []image.Image `json:"images,omitempty" yaml:"images,omitempty"`
 
+	// Replicas is a list of {resourcename, count} that allows for simpler replica
+	// specification. This can also be done with a patch.
+	Replicas []replica.Replica `json:"replicas,omitempty" yaml:"replicas,omitempty"`
+
 	// Vars allow things modified by kustomize to be injected into a
 	// container specification. A var is a name (e.g. FOO) associated
 	// with a field in a specific resource instance.  The field must