Add support for Kustomize components

Fix #753

Signed-off-by: Kristian Klausen <kristian@klausen.dk>

api/v1beta2/kustomization_types.go

@@ -153,6 +153,10 @@ type KustomizationSpec struct {
 	// +kubebuilder:validation:Enum=none;client;server
 	// +optional
 	Validation string `json:"validation,omitempty"`
+
+	// Components specifies relative paths to specifications of other Components
+	// +optional
+	Components []string `json:"components,omitempty"`
 }
 
 // Decryption defines how decryption is handled for Kubernetes manifests.

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

@@ -585,6 +585,12 @@ spec:
             description: KustomizationSpec defines the configuration to calculate
               the desired state from a Source using Kustomize.
             properties:
+              components:
+                description: Components specifies relative paths to specifications
+                  of other Components
+                items:
+                  type: string
+                type: array
               decryption:
                 description: Decrypt Kubernetes secrets before applying them on the
                   cluster.

docs/spec/v1beta2/kustomization.md

@@ -556,6 +556,7 @@ offering support for the following Kustomize directives:
 - [namespace](https://kubectl.docs.kubernetes.io/references/kustomize/kustomization/namespace/)
 - [patches](https://kubectl.docs.kubernetes.io/references/kustomize/kustomization/patches/)
 - [images](https://kubectl.docs.kubernetes.io/references/kustomize/kustomization/images/)
+- [components](https://kubectl.docs.kubernetes.io/references/kustomize/kustomization/components/)
 
 ### Target namespace
 
@@ -654,6 +655,31 @@ spec:
     digest: sha256:24a0c4b4a4c0eb97a1aabb8e29f18e917d05abfe1b7a7c07857230879ce7d3d3
 ```
 
+### Components
+
+To add [Kustomize `components` entries](https://kubectl.docs.kubernetes.io/references/kustomize/kustomization/components/)
+to the configuration, and use reusable pieces of configuration logic that can
+be included from multiple overlays, `spec.components` can be defined:
+
+```yaml
+apiVersion: kustomize.toolkit.fluxcd.io/v1beta2
+kind: Kustomization
+metadata:
+  name: podinfo
+  namespace: flux-system
+spec:
+  # ...omitted for brevity
+  components:
+  - ingress
+  - tls
+```
+
+**Note:** The component paths must be local and relative.
+
+**Warning:** Components are a alpha feature in Kustomize and are therefore
+considered experimental in Flux. No guarantees are provided and the feature may
+be modified in backwards incompatible ways or removed without warning.
+
 ## Variable substitution
 
 With `spec.postBuild.substitute` you can provide a map of key/value pairs holding the

internal/generator/generator.go

@@ -79,6 +79,13 @@ func (kg *KustomizeGenerator) WriteFile(dirPath string) (string, error) {
 		})
 	}
 
+	for _, m := range kg.kustomization.Spec.Components {
+		if !isLocalRelativePath(m) {
+			return "", fmt.Errorf("component path '%s' must be local and relative", m)
+		}
+		kus.Components = append(kus.Components, m)
+	}
+
 	for _, m := range kg.kustomization.Spec.PatchesStrategicMerge {
 		kus.PatchesStrategicMerge = append(kus.PatchesStrategicMerge, kustypes.PatchStrategicMerge(m.Raw))
 	}
@@ -234,3 +241,21 @@ func adaptSelector(selector *kustomize.Selector) (output *kustypes.Selector) {
 	}
 	return
 }
+
+func isLocalRelativePath(path string) bool {
+	// From: https://github.com/kubernetes-sigs/kustomize/blob/84bd402cc0662c5df3f109c4f80c22611243c5f9/api/internal/git/repospec.go#L231-L239
+	// with "file://" removed/
+	for _, p := range []string{
+		// Order matters here.
+		"git::", "gh:", "ssh://", "https://", "http://",
+		"git@", "github.com:", "github.com/"} {
+		if len(p) < len(path) && strings.ToLower(path[:len(p)]) == p {
+			return false
+		}
+	}
+
+	if filepath.IsAbs(path) || filepath.IsAbs(strings.TrimPrefix(strings.ToLower(path), "file://")) {
+		return false
+	}
+	return true
+}

internal/generator/generator_test.go

@@ -93,3 +93,52 @@ func TestGenerator_WriteFile(t *testing.T) {
 		})
 	}
 }
+
+func TestGenerator_Components(t *testing.T) {
+	tests := []struct {
+		name               string
+		dir                string
+		fluxComponents     []string
+		expectedComponents []string
+	}{
+		{
+			name:               "test kustomization.yaml with components and Flux Kustomization without components",
+			dir:                "components",
+			fluxComponents:     []string{},
+			expectedComponents: []string{"componentA"},
+		},
+		{
+			name:               "test kustomization.yaml without components and Flux Kustomization with components",
+			dir:                "zero-components",
+			fluxComponents:     []string{"componentB", "componentC"},
+			expectedComponents: []string{"componentB", "componentC"},
+		},
+		{
+			name:               "test kustomization.yaml with components and Flux Kustomization with components",
+			dir:                "components",
+			fluxComponents:     []string{"componentB", "componentC"},
+			expectedComponents: []string{"componentA", "componentB", "componentC"},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			g := NewWithT(t)
+			tmpDir := t.TempDir()
+			g.Expect(copy.Copy("./testdata/components", tmpDir)).To(Succeed())
+			ks := v1beta2.Kustomization{
+				Spec: v1beta2.KustomizationSpec{
+					Components: tt.fluxComponents,
+				},
+			}
+			kfile, err := NewGenerator(filepath.Join(tmpDir, tt.dir), &ks).WriteFile(filepath.Join(tmpDir, tt.dir))
+			g.Expect(err).ToNot(HaveOccurred())
+
+			kfileYAML, err := os.ReadFile(kfile)
+			g.Expect(err).ToNot(HaveOccurred())
+			var k kustypes.Kustomization
+			g.Expect(k.Unmarshal(kfileYAML)).To(Succeed())
+			g.Expect(k.Components).Should(Equal(tt.expectedComponents))
+		})
+	}
+}

internal/generator/testdata/components/components/kustomization.yaml

@@ -0,0 +1,7 @@
+---
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - configmap.yaml
+components:
+  - componentA

internal/generator/testdata/components/zero-components/kustomization.yaml

@@ -0,0 +1,5 @@
+---
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - configmap.yaml