From 5000a2e5035ab39eece7d74001fbce68a3839087 Mon Sep 17 00:00:00 2001
From: Damien Robichaud <damienr74@gmail.com>
Date: Wed, 29 May 2019 18:27:39 -0700
Subject: [PATCH 1/3] Implement replica transformer as patch alternative

---
 pkg/replica/replica.go                        | 13 +++++
 pkg/target/kusttarget_configplugin.go         | 22 +++++++
 pkg/transformers/config/transformerconfig.go  |  2 +
 pkg/types/kustomization.go                    |  5 ++
 plugin/builtin/ReplicaCountTransformer.go     | 57 ++++++++++++++++++
 .../ReplicaCountTransformer.go                | 58 +++++++++++++++++++
 .../ReplicaCountTransformer_test.go           | 49 ++++++++++++++++
 7 files changed, 206 insertions(+)
 create mode 100644 pkg/replica/replica.go
 create mode 100644 plugin/builtin/ReplicaCountTransformer.go
 create mode 100644 plugin/builtin/replicacounttransformer/ReplicaCountTransformer.go
 create mode 100644 plugin/builtin/replicacounttransformer/ReplicaCountTransformer_test.go

diff --git a/pkg/replica/replica.go b/pkg/replica/replica.go
new file mode 100644
index 000000000..90ce319e6
--- /dev/null
+++ b/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"`
+}
diff --git a/pkg/target/kusttarget_configplugin.go b/pkg/target/kusttarget_configplugin.go
index 71dcd0454..5afe53541 100644
--- a/pkg/target/kusttarget_configplugin.go
+++ b/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
diff --git a/pkg/transformers/config/transformerconfig.go b/pkg/transformers/config/transformerconfig.go
index a00c6da66..3e47d1401 100644
--- a/pkg/transformers/config/transformerconfig.go
+++ b/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
diff --git a/pkg/types/kustomization.go b/pkg/types/kustomization.go
index 86fd1f985..acaa47c5f 100644
--- a/pkg/types/kustomization.go
+++ b/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
diff --git a/plugin/builtin/ReplicaCountTransformer.go b/plugin/builtin/ReplicaCountTransformer.go
new file mode 100644
index 000000000..41412deb0
--- /dev/null
+++ b/plugin/builtin/ReplicaCountTransformer.go
@@ -0,0 +1,57 @@
+// Code generated by pluginator on ReplicaCountTransformer; DO NOT EDIT.
+package builtin
+
+import (
+	"github.com/pkg/errors"
+	"sigs.k8s.io/kustomize/pkg/ifc"
+	"sigs.k8s.io/kustomize/pkg/replica"
+	"sigs.k8s.io/kustomize/pkg/resid"
+	"sigs.k8s.io/kustomize/pkg/resmap"
+	"sigs.k8s.io/kustomize/pkg/transformers/config"
+	"sigs.k8s.io/yaml"
+)
+
+// Find matching replicas declarations and replace
+// the count.
+type ReplicaCountTransformerPlugin struct {
+	Replica    replica.Replica    `json:"replica,omitempty" yaml:"replica,omitempty"`
+	FieldSpecs []config.FieldSpec `json:"fieldSpecs,omitempty" yaml:"fieldSpecs,omitempty"`
+}
+
+func NewReplicaCountTransformerPlugin() *ReplicaCountTransformerPlugin {
+	return &ReplicaCountTransformerPlugin{}
+}
+
+func (p *ReplicaCountTransformerPlugin) Config(
+	ldr ifc.Loader, rf *resmap.Factory, c []byte) (err error) {
+
+	p.Replica = replica.Replica{}
+	p.FieldSpecs = nil
+	return yaml.Unmarshal(c, p)
+}
+
+func (p *ReplicaCountTransformerPlugin) Transform(m resmap.ResMap) error {
+	matcher := func(r resid.ResId) bool {
+		return r.ItemId.Name == p.Replica.Name
+	}
+
+	for _, r := range m.GetMatchingIds(matcher) {
+		kMap := m[r].Kunstructured.Map()
+
+		specInterface, ok := kMap["spec"]
+		if !ok {
+			return errors.New("'spec' not specified, replicas cannot be modified")
+		}
+
+		if spec, ok := specInterface.(map[string]interface{}); ok {
+			spec["replicas"] = p.Replica.Count
+			kMap["spec"] = spec
+		} else {
+			return errors.New("'spec' not structured as expected")
+		}
+
+		m[r].Kunstructured.SetMap(kMap)
+	}
+
+	return nil
+}
diff --git a/plugin/builtin/replicacounttransformer/ReplicaCountTransformer.go b/plugin/builtin/replicacounttransformer/ReplicaCountTransformer.go
new file mode 100644
index 000000000..d78e0237b
--- /dev/null
+++ b/plugin/builtin/replicacounttransformer/ReplicaCountTransformer.go
@@ -0,0 +1,58 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+//go:generate go run sigs.k8s.io/kustomize/plugin/pluginator
+package main
+
+import (
+	"github.com/pkg/errors"
+	"sigs.k8s.io/kustomize/pkg/ifc"
+	"sigs.k8s.io/kustomize/pkg/replica"
+	"sigs.k8s.io/kustomize/pkg/resid"
+	"sigs.k8s.io/kustomize/pkg/resmap"
+	"sigs.k8s.io/kustomize/pkg/transformers/config"
+	"sigs.k8s.io/yaml"
+)
+
+// Find matching replicas declarations and replace the count.
+// Eases the kustomization configuration of replica changes.
+type plugin struct {
+	Replica    replica.Replica    `json:"replica,omitempty" yaml:"replica,omitempty"`
+	FieldSpecs []config.FieldSpec `json:"fieldSpecs,omitempty" yaml:"fieldSpecs,omitempty"`
+}
+
+var KustomizePlugin plugin
+
+func (p *plugin) Config(
+	ldr ifc.Loader, rf *resmap.Factory, c []byte) (err error) {
+
+	p.Replica = replica.Replica{}
+	p.FieldSpecs = nil
+	return yaml.Unmarshal(c, p)
+}
+
+func (p *plugin) Transform(m resmap.ResMap) error {
+	matcher := func(r resid.ResId) bool {
+		return r.ItemId.Name == p.Replica.Name
+	}
+
+	for _, r := range m.GetMatchingIds(matcher) {
+		kMap := m[r].Kunstructured.Map()
+
+		specInterface, ok := kMap["spec"]
+		if !ok {
+			return errors.New("'spec' not specified, replicas cannot be modified")
+		}
+
+		if spec, ok := specInterface.(map[string]interface{}); ok {
+			spec["replicas"] = p.Replica.Count
+			kMap["spec"] = spec
+		} else {
+			return errors.New("'spec' not structured as expected")
+		}
+
+		m[r].Kunstructured.SetMap(kMap)
+	}
+
+	return nil
+}
diff --git a/plugin/builtin/replicacounttransformer/ReplicaCountTransformer_test.go b/plugin/builtin/replicacounttransformer/ReplicaCountTransformer_test.go
new file mode 100644
index 000000000..3d22c30f5
--- /dev/null
+++ b/plugin/builtin/replicacounttransformer/ReplicaCountTransformer_test.go
@@ -0,0 +1,49 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package main_test
+
+import (
+	"testing"
+
+	"sigs.k8s.io/kustomize/pkg/kusttest"
+	"sigs.k8s.io/kustomize/plugin"
+)
+
+func TestReplicaCountTransformer(t *testing.T) {
+	tc := plugin.NewEnvForTest(t).Set()
+	defer tc.Reset()
+
+	tc.BuildGoPlugin(
+		"builtin", "", "ReplicaCountTransformer")
+
+	th := kusttest_test.NewKustTestPluginHarness(t, "/app")
+
+	rm := th.LoadAndRunTransformer(`
+apiVersion: builtin
+kind: ReplicaCountTransformer
+metadata:
+  name: notImportantHere
+replica:
+  name: deploy1
+  count: 23
+`, `
+group: apps
+apiVersion: v1
+kind: Deployment
+metadata:
+  name: deploy1
+spec:
+  replicas: 1
+`)
+
+	th.AssertActualEqualsExpected(rm, `
+apiVersion: v1
+group: apps
+kind: Deployment
+metadata:
+  name: deploy1
+spec:
+  replicas: 23
+`)
+}

From d4842ebd90ec43e69a8be1ddee3aab51bbd6e871 Mon Sep 17 00:00:00 2001
From: Damien Robichaud <damienr74@gmail.com>
Date: Fri, 31 May 2019 11:20:36 -0700
Subject: [PATCH 2/3] Cleanup the replica plugin implementation.

---
 pkg/replica/replica.go                        | 13 -------
 pkg/target/kusttarget_configplugin.go         |  6 ++--
 pkg/transformers/config/transformerconfig.go  |  2 --
 pkg/types/kustomization.go                    | 15 ++++++--
 plugin/builtin/ReplicaCountTransformer.go     | 36 ++++++++++---------
 .../ReplicaCountTransformer.go                | 32 +++++++++--------
 6 files changed, 51 insertions(+), 53 deletions(-)
 delete mode 100644 pkg/replica/replica.go

diff --git a/pkg/replica/replica.go b/pkg/replica/replica.go
deleted file mode 100644
index 90ce319e6..000000000
--- a/pkg/replica/replica.go
+++ /dev/null
@@ -1,13 +0,0 @@
-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"`
-}
diff --git a/pkg/target/kusttarget_configplugin.go b/pkg/target/kusttarget_configplugin.go
index 5afe53541..a6371089a 100644
--- a/pkg/target/kusttarget_configplugin.go
+++ b/pkg/target/kusttarget_configplugin.go
@@ -7,7 +7,6 @@ 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"
@@ -80,6 +79,7 @@ func (kt *KustTarget) configureBuiltinTransformers(
 		}
 		result = append(result, r...)
 	}
+
 	return result, nil
 }
 
@@ -239,12 +239,10 @@ func (kt *KustTarget) configureBuiltinReplicaCountTransformer(
 	tConfig *config.TransformerConfig) (
 	result []transformers.Transformer, err error) {
 	var c struct {
-		Replica    replica.Replica
-		FieldSpecs []config.FieldSpec
+		Replica types.Replica
 	}
 	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 {
diff --git a/pkg/transformers/config/transformerconfig.go b/pkg/transformers/config/transformerconfig.go
index 3e47d1401..a00c6da66 100644
--- a/pkg/transformers/config/transformerconfig.go
+++ b/pkg/transformers/config/transformerconfig.go
@@ -35,7 +35,6 @@ 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
@@ -62,7 +61,6 @@ 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
diff --git a/pkg/types/kustomization.go b/pkg/types/kustomization.go
index acaa47c5f..eb6fc2af2 100644
--- a/pkg/types/kustomization.go
+++ b/pkg/types/kustomization.go
@@ -22,7 +22,6 @@ import (
 
 	"sigs.k8s.io/kustomize/pkg/gvk"
 	"sigs.k8s.io/kustomize/pkg/image"
-	"sigs.k8s.io/kustomize/pkg/replica"
 )
 
 const (
@@ -82,7 +81,7 @@ type Kustomization struct {
 
 	// 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"`
+	Replicas []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
@@ -360,3 +359,15 @@ type PatchTarget struct {
 // stategic merge patch with the format
 // https://github.com/kubernetes/community/blob/master/contributors/devel/strategic-merge-patch.md
 type PatchStrategicMerge string
+
+// 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"`
+}
diff --git a/plugin/builtin/ReplicaCountTransformer.go b/plugin/builtin/ReplicaCountTransformer.go
index 41412deb0..018079189 100644
--- a/plugin/builtin/ReplicaCountTransformer.go
+++ b/plugin/builtin/ReplicaCountTransformer.go
@@ -2,20 +2,24 @@
 package builtin
 
 import (
-	"github.com/pkg/errors"
+	"fmt"
+
 	"sigs.k8s.io/kustomize/pkg/ifc"
-	"sigs.k8s.io/kustomize/pkg/replica"
 	"sigs.k8s.io/kustomize/pkg/resid"
 	"sigs.k8s.io/kustomize/pkg/resmap"
-	"sigs.k8s.io/kustomize/pkg/transformers/config"
+	"sigs.k8s.io/kustomize/pkg/types"
 	"sigs.k8s.io/yaml"
 )
 
-// Find matching replicas declarations and replace
-// the count.
+const (
+	fldReplica = "replicas"
+	fldSpec    = "spec"
+)
+
+// Find matching replicas declarations and replace the count.
+// Eases the kustomization configuration of replica changes.
 type ReplicaCountTransformerPlugin struct {
-	Replica    replica.Replica    `json:"replica,omitempty" yaml:"replica,omitempty"`
-	FieldSpecs []config.FieldSpec `json:"fieldSpecs,omitempty" yaml:"fieldSpecs,omitempty"`
+	Replica types.Replica `json:"replica,omitempty" yaml:"replica,omitempty"`
 }
 
 func NewReplicaCountTransformerPlugin() *ReplicaCountTransformerPlugin {
@@ -25,8 +29,7 @@ func NewReplicaCountTransformerPlugin() *ReplicaCountTransformerPlugin {
 func (p *ReplicaCountTransformerPlugin) Config(
 	ldr ifc.Loader, rf *resmap.Factory, c []byte) (err error) {
 
-	p.Replica = replica.Replica{}
-	p.FieldSpecs = nil
+	p.Replica = types.Replica{}
 	return yaml.Unmarshal(c, p)
 }
 
@@ -36,21 +39,20 @@ func (p *ReplicaCountTransformerPlugin) Transform(m resmap.ResMap) error {
 	}
 
 	for _, r := range m.GetMatchingIds(matcher) {
-		kMap := m[r].Kunstructured.Map()
+		kMap := m[r].Map()
 
-		specInterface, ok := kMap["spec"]
+		specInterface, ok := kMap[fldSpec]
 		if !ok {
-			return errors.New("'spec' not specified, replicas cannot be modified")
+			return fmt.Errorf("object %s missing field %s, cannot update %s",
+				p.Replica.Name, fldSpec, fldReplica)
 		}
 
 		if spec, ok := specInterface.(map[string]interface{}); ok {
-			spec["replicas"] = p.Replica.Count
-			kMap["spec"] = spec
+			spec[fldReplica] = p.Replica.Count
+			kMap[fldSpec] = spec
 		} else {
-			return errors.New("'spec' not structured as expected")
+			return fmt.Errorf("object %s has a malformed %s", p.Replica.Name, fldSpec)
 		}
-
-		m[r].Kunstructured.SetMap(kMap)
 	}
 
 	return nil
diff --git a/plugin/builtin/replicacounttransformer/ReplicaCountTransformer.go b/plugin/builtin/replicacounttransformer/ReplicaCountTransformer.go
index d78e0237b..d50fc2af6 100644
--- a/plugin/builtin/replicacounttransformer/ReplicaCountTransformer.go
+++ b/plugin/builtin/replicacounttransformer/ReplicaCountTransformer.go
@@ -5,20 +5,24 @@
 package main
 
 import (
-	"github.com/pkg/errors"
+	"fmt"
+
 	"sigs.k8s.io/kustomize/pkg/ifc"
-	"sigs.k8s.io/kustomize/pkg/replica"
 	"sigs.k8s.io/kustomize/pkg/resid"
 	"sigs.k8s.io/kustomize/pkg/resmap"
-	"sigs.k8s.io/kustomize/pkg/transformers/config"
+	"sigs.k8s.io/kustomize/pkg/types"
 	"sigs.k8s.io/yaml"
 )
 
+const (
+	fldReplica = "replicas"
+	fldSpec    = "spec"
+)
+
 // Find matching replicas declarations and replace the count.
 // Eases the kustomization configuration of replica changes.
 type plugin struct {
-	Replica    replica.Replica    `json:"replica,omitempty" yaml:"replica,omitempty"`
-	FieldSpecs []config.FieldSpec `json:"fieldSpecs,omitempty" yaml:"fieldSpecs,omitempty"`
+	Replica types.Replica `json:"replica,omitempty" yaml:"replica,omitempty"`
 }
 
 var KustomizePlugin plugin
@@ -26,8 +30,7 @@ var KustomizePlugin plugin
 func (p *plugin) Config(
 	ldr ifc.Loader, rf *resmap.Factory, c []byte) (err error) {
 
-	p.Replica = replica.Replica{}
-	p.FieldSpecs = nil
+	p.Replica = types.Replica{}
 	return yaml.Unmarshal(c, p)
 }
 
@@ -37,21 +40,20 @@ func (p *plugin) Transform(m resmap.ResMap) error {
 	}
 
 	for _, r := range m.GetMatchingIds(matcher) {
-		kMap := m[r].Kunstructured.Map()
+		kMap := m[r].Map()
 
-		specInterface, ok := kMap["spec"]
+		specInterface, ok := kMap[fldSpec]
 		if !ok {
-			return errors.New("'spec' not specified, replicas cannot be modified")
+			return fmt.Errorf("object %s missing field %s, cannot update %s",
+				p.Replica.Name, fldSpec, fldReplica)
 		}
 
 		if spec, ok := specInterface.(map[string]interface{}); ok {
-			spec["replicas"] = p.Replica.Count
-			kMap["spec"] = spec
+			spec[fldReplica] = p.Replica.Count
+			kMap[fldSpec] = spec
 		} else {
-			return errors.New("'spec' not structured as expected")
+			return fmt.Errorf("object %s has a malformed %s", p.Replica.Name, fldSpec)
 		}
-
-		m[r].Kunstructured.SetMap(kMap)
 	}
 
 	return nil

From d925939795401015b3bfa733d734ce1880b29f6a Mon Sep 17 00:00:00 2001
From: Damien Robichaud <damienr74@gmail.com>
Date: Fri, 31 May 2019 13:29:04 -0700
Subject: [PATCH 3/3] Add documentation for the replicas transform

---
 docs/fields.md | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/docs/fields.md b/docs/fields.md
index 39d4e5dd3..48f9832a1 100644
--- a/docs/fields.md
+++ b/docs/fields.md
@@ -36,6 +36,7 @@ What transformations (customizations) should be applied?
 | [nameSuffix](#namesuffix) | string | The value is appended to the names of all resources. |
 | [commonLabels](#commonlabels) | string | Adds annotions (non-identifying metadata) to add all resources. Like labels, these are key value pairs. |
 | [images](#images) | list | Images modify the name, tags and/or digest for images without creating patches. |
+| [replicas](#replicas) | list | Replicas modify the number of replicas for a resource without creating patches. |
 |[patchesStrategicMerge](#patchesstrategicmerge)| list |Each entry in this list should resolve to a partial or complete resource definition file.|
 |[patchesJson6902](#patchesjson6902)| list  |Each entry in this list should resolve to a kubernetes object and a JSON patch that will be applied to the object.|
 |[transformers](#transformers)|list|[plugin](plugins.md) configuration files|
@@ -236,6 +237,24 @@ images:
   digest: sha256:24a0c4b4a4c0eb97a1aabb8e29f18e917d05abfe1b7a7c07857230879ce7d3d3
 ```
 
+### replicas
+
+Replicas modify the number of replicas for a resource without creating patches.
+E.g. Given this kubernetes Deployment fragment:
+```
+metadata:
+  name: deployment-name
+spec:
+  replicas: 3
+```
+
+one can change the number of replicas to 5 with the following *kustomization*:
+```
+replicas:
+- name: deployment-name
+  count: 5
+```
+note that replicas is a list, so many replicas can be modified at the same time.
 
 ### kind