Generate label transformers for the prune selectors

README.md

@@ -7,7 +7,7 @@
 
 The kustomize-controller is a continuous delivery tool for Kubernetes, specialized in running 
 CD pipelines inside the cluster for workloads and infrastructure manifests
-generated with Kustomize coming from source control systems.
+coming from source control systems.
 
 ![overview](docs/diagrams/fluxcd-kustomize-source-controllers.png)
 

api/v1alpha1/kustomization_types.go

@@ -32,7 +32,7 @@ type KustomizationSpec struct {
 
 	// When enabled, the kustomization.yaml is automatically generated
 	// for all the Kubernetes manifests in the specified path and sub-directories.
-	// The generated kustomization.yaml will have common labels taken from the prune field.
+	// The generated kustomization.yaml contains a label transformer matching the prune field.
 	// +optional
 	Generate bool `json:"generate,omitempty"`
 

config/crd/bases/kustomize.fluxcd.io_kustomizations.yaml

@@ -55,7 +55,7 @@ spec:
             generate:
               description: When enabled, the kustomization.yaml is automatically generated
                 for all the Kubernetes manifests in the specified path and sub-directories.
-                The generated kustomization.yaml will have common labels taken from
+                The generated kustomization.yaml contains a label transformer matching
                 the prune field.
               type: boolean
             healthChecks:

controllers/kustomization_controller.go

@@ -17,6 +17,8 @@ limitations under the License.
 package controllers
 
 import (
+	"bufio"
+	"bytes"
 	"context"
 	"errors"
 	"fmt"
@@ -25,6 +27,7 @@ import (
 	"os/exec"
 	"path"
 	"strings"
+	"text/template"
 	"time"
 
 	"github.com/go-logr/logr"
@@ -282,14 +285,8 @@ func (r *KustomizationReconciler) generate(kustomization kustomizev1.Kustomizati
 	ctx, cancel := context.WithTimeout(context.Background(), timeout)
 	defer cancel()
 
-	labels := ""
-	if prune := kustomization.Spec.Prune; prune != "" {
-		labels = fmt.Sprintf("--labels %s", strings.ReplaceAll(prune, "=", ":"))
-	}
-
 	dirPath := path.Join(tmpDir, kustomization.Spec.Path)
-	cmd := fmt.Sprintf("cd %s && kustomize create --autodetect --recursive %s",
-		dirPath, labels)
+	cmd := fmt.Sprintf("cd %s && kustomize create --autodetect --recursive", dirPath)
 	command := exec.CommandContext(ctx, "/bin/sh", "-c", cmd)
 	output, err := command.CombinedOutput()
 	if err != nil {
@@ -298,6 +295,86 @@ func (r *KustomizationReconciler) generate(kustomization kustomizev1.Kustomizati
 		}
 		return fmt.Errorf("kustomize create failed: %s", string(output))
 	}
+
+	if err := r.generateLabelTransformer(kustomization, dirPath); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (r *KustomizationReconciler) generateLabelTransformer(kustomization kustomizev1.Kustomization, dirPath string) error {
+	labelTransformer := `
+apiVersion: builtin
+kind: LabelTransformer
+metadata:
+  name: labels
+labels:
+{{- range $key, $value := . }}
+  {{ $key }}: {{ $value }}
+{{- end }}
+fieldSpecs:
+  - path: metadata/labels
+    create: true
+`
+
+	transformers := `
+transformers:
+  - gc-labels.yaml
+`
+
+	prune := kustomization.Spec.Prune
+	if prune == "" {
+		return nil
+	}
+
+	// transform prune into label selectors
+	selectors := make(map[string]string)
+	for _, ls := range strings.Split(prune, ",") {
+		if kv := strings.Split(ls, "="); len(kv) == 2 {
+			selectors[kv[0]] = kv[1]
+		}
+	}
+
+	t, err := template.New("tmpl").Parse(labelTransformer)
+	if err != nil {
+		return fmt.Errorf("labelTransformer template parsing failed: %w", err)
+	}
+
+	var data bytes.Buffer
+	writer := bufio.NewWriter(&data)
+	if err := t.Execute(writer, selectors); err != nil {
+		return fmt.Errorf("labelTransformer template excution failed: %w", err)
+	}
+
+	if err := writer.Flush(); err != nil {
+		return fmt.Errorf("labelTransformer flush failed: %w", err)
+	}
+
+	file, err := os.Create(path.Join(dirPath, "gc-labels.yaml"))
+	if err != nil {
+		return fmt.Errorf("labelTransformer create failed: %w", err)
+	}
+	defer file.Close()
+
+	if _, err := file.WriteString(data.String()); err != nil {
+		return fmt.Errorf("labelTransformer write failed: %w", err)
+	}
+
+	if err := file.Sync(); err != nil {
+		return fmt.Errorf("labelTransformer sync failed: %w", err)
+	}
+
+	kfile, err := os.OpenFile(path.Join(dirPath, "kustomization.yaml"), os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+	if err != nil {
+		return fmt.Errorf("kustomization file open failed: %w", err)
+	}
+	defer kfile.Close()
+
+	if _, err := kfile.WriteString(transformers); err != nil {
+		return fmt.Errorf("kustomization file append failed: %w", err)
+	}
+
 	return nil
 }
 

controllers/kustomization_predicate.go

@@ -20,7 +20,6 @@ import (
 	"context"
 	"fmt"
 	"os/exec"
-	"strings"
 
 	"github.com/go-logr/logr"
 	"sigs.k8s.io/controller-runtime/pkg/event"
@@ -76,12 +75,12 @@ func (gc KustomizationGarbageCollectPredicate) Delete(e event.DeleteEvent) bool
 			command := exec.CommandContext(ctx, "/bin/sh", "-c", cmd)
 			if output, err := command.CombinedOutput(); err != nil {
 				gc.Log.Error(err, "Garbage collection failed",
-					"output", string(output),
-					strings.ToLower(k.Kind), fmt.Sprintf("%s/%s", k.GetNamespace(), k.GetName()))
+					"kustomization", fmt.Sprintf("%s/%s", k.GetNamespace(), k.GetName()),
+					"output", string(output))
 			} else {
 				gc.Log.Info("Garbage collection completed",
-					"output", string(output),
-					strings.ToLower(k.Kind), fmt.Sprintf("%s/%s", k.GetNamespace(), k.GetName()))
+					"kustomization", fmt.Sprintf("%s/%s", k.GetNamespace(), k.GetName()),
+					"output", string(output))
 			}
 		}
 	}

docs/spec/v1alpha1/kustomization.md

@@ -18,7 +18,7 @@ type KustomizationSpec struct {
 
 	// When enabled, the kustomization.yaml is automatically generated
 	// for all the Kubernetes manifests in the specified path and sub-directories.
-	// The generated kustomization.yaml will have common labels taken from the prune field.
+	// The generated kustomization.yaml contains a label transformer matching the prune field.
 	// +optional
 	Generate bool `json:"generate,omitempty"`
 
@@ -119,16 +119,18 @@ Source supported types:
 
 > **Note** that the source should contain the kustomization.yaml and all the
 > Kubernetes manifests and configuration files referenced in the kustomization.yaml.
-> If your repository contains only plain Kubernetes then you can enable kustomization.yaml generation.
+> If your repository contains only plain manifests, then you should enable kustomization.yaml generation.
 
 ## Generate kustomization.yaml
 
 If your repository contains plain Kubernetes manifests, you can configure the
 controller to generate a `kustomization.yaml` by setting `spec.generate` to `true`.
 
-When `spec.generate` is enabled, the `kustomization.yaml` is automatically generated for
+When `spec.generate` is enabled, the `kustomization.yaml` file is automatically generated for
 all the Kubernetes manifests in the `spec.path` and sub-directories.
-The generated `kustomization.yaml` will have common labels taken from the `spec.prune` field.
+
+If the `spec.prune` is not empty, the controller generates a label transformer to enable
+[garbage collection](#garbage-collection).
 
 ## Reconciliation
 
@@ -162,8 +164,8 @@ but are missing from the current apply, are removed from cluster automatically.
 Garbage collection is also performed when a Kustomization object is deleted,
 triggering a removal of all Kubernetes objects previously applied on the cluster.
 
-Tpo enable garbage collection, all Kubernetes objects must have a common label that matches the `spec.prune`
-[label selector](https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/).
+Tpo enable garbage collection, all Kubernetes objects must have common labels matching the `spec.prune`
+[label selectors](https://kubernetes.io/docs/concepts/overview/working-with-objects/labels/).
 
 For example, `prune: env=dev,app=frontend` requires a `kustomization.yaml` with `commonLabels`:
 
@@ -175,9 +177,33 @@ commonLabels:
   app: frontend
 ```
 
-> **Note** that each kustomization must have a unique combination of labels values, otherwise the 
+> **Note** that each kustomization must have a unique combination of label key/values, otherwise the 
 > garbage collection will remove resources outside of the kustomization scope.
 
+Another option to label all Kubernetes objects, is with label transformers:
+
+```yaml
+apiVersion: builtin
+kind: LabelTransformer
+metadata:
+  name: labels
+labels:
+  env: dev
+  app: frontend
+fieldSpecs:
+  - path: metadata/labels
+    create: true
+```
+
+Save the above file as `labels.yaml` and add it to your `kustomization.yaml`:
+
+```yaml
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+transformers:
+  - labels.yaml
+```
+
 ## Health assessment
 
 A kustomization can contain a series of health checks used to determine the