Support force-building metadata layers into snapshot (#1731)

* feat: add support for forcing build metadata

* Chore: Added snapshot forceBuildMetadata flag tests.

cmd/executor/cmd/root.go

@@ -216,6 +216,7 @@ func addKanikoOptionsFlags() {
 	RootCmd.PersistentFlags().Var(&opts.Git, "git", "Branch to clone if build context is a git repository")
 	RootCmd.PersistentFlags().BoolVarP(&opts.CacheCopyLayers, "cache-copy-layers", "", false, "Caches copy layers")
 	RootCmd.PersistentFlags().VarP(&opts.IgnorePaths, "ignore-path", "", "Ignore these paths when taking a snapshot. Set it repeatedly for multiple paths.")
+	RootCmd.PersistentFlags().BoolVarP(&opts.ForceBuildMetadata, "force-build-metadata", "", false, "Force add metadata layers to build image")
 }
 
 // addHiddenFlags marks certain flags as hidden from the executor help text

pkg/config/options.go

@@ -74,6 +74,7 @@ type KanikoOptions struct {
 	Git                    KanikoGitOptions
 	IgnorePaths            multiArg
 	ImageFSExtractRetry    int
+	ForceBuildMetadata	   bool
 }
 
 type KanikoGitOptions struct {

pkg/executor/build.go

@@ -60,7 +60,7 @@ type cachePusher func(*config.KanikoOptions, string, string, string) error
 type snapShotter interface {
 	Init() error
 	TakeSnapshotFS() (string, error)
-	TakeSnapshot([]string, bool) (string, error)
+	TakeSnapshot([]string, bool, bool) (string, error)
 }
 
 // stageBuilder contains all fields necessary to build one stage of a Dockerfile
@@ -375,7 +375,8 @@ func (s *stageBuilder) build() error {
 		files = command.FilesToSnapshot()
 		timing.DefaultRun.Stop(t)
 
-		if !s.shouldTakeSnapshot(index, command.MetadataOnly()) {
+		if !s.shouldTakeSnapshot(index, command.MetadataOnly()) && !s.opts.ForceBuildMetadata{
+			logrus.Debugf("build: skipping snapshot for [%v]" , command.String())
 			continue
 		}
 		if isCacheCommand {
@@ -429,7 +430,7 @@ func (s *stageBuilder) takeSnapshot(files []string, shdDelete bool) (string, err
 	} else {
 		// Volumes are very weird. They get snapshotted in the next command.
 		files = append(files, util.Volumes()...)
-		snapshot, err = s.snapshotter.TakeSnapshot(files, shdDelete)
+		snapshot, err = s.snapshotter.TakeSnapshot(files, shdDelete, s.opts.ForceBuildMetadata)
 	}
 	timing.DefaultRun.Stop(t)
 	return snapshot, err
@@ -473,7 +474,7 @@ func (s *stageBuilder) saveSnapshotToLayer(tarPath string) (v1.Layer, error) {
 	if err != nil {
 		return nil, errors.Wrap(err, "tar file path does not exist")
 	}
-	if fi.Size() <= emptyTarSize {
+	if fi.Size() <= emptyTarSize && !s.opts.ForceBuildMetadata{
 		logrus.Info("No files were changed, appending empty layer to config. No layer added to image.")
 		return nil, nil
 	}

pkg/snapshot/snapshot.go

@@ -35,6 +35,9 @@ import (
 // For testing
 var snapshotPathPrefix = ""
 
+// for user layer flag
+var addUserLayer bool = true
+
 // Snapshotter holds the root directory from which to take snapshots, and a list of snapshots taken
 type Snapshotter struct {
 	l          *LayeredMap
@@ -60,7 +63,7 @@ func (s *Snapshotter) Key() (string, error) {
 
 // TakeSnapshot takes a snapshot of the specified files, avoiding directories in the ignorelist, and creates
 // a tarball of the changed files. Return contents of the tarball, and whether or not any files were changed
-func (s *Snapshotter) TakeSnapshot(files []string, shdCheckDelete bool) (string, error) {
+func (s *Snapshotter) TakeSnapshot(files []string, shdCheckDelete bool, forceBuildMetadata bool) (string, error) {
 	f, err := ioutil.TempFile(config.KanikoDir, "")
 	if err != nil {
 		return "", err
@@ -68,7 +71,7 @@ func (s *Snapshotter) TakeSnapshot(files []string, shdCheckDelete bool) (string,
 	defer f.Close()
 
 	s.l.Snapshot()
-	if len(files) == 0 {
+	if len(files) == 0 && !forceBuildMetadata {
 		logrus.Info("No files changed in this command, skipping snapshotting.")
 		return "", nil
 	}

pkg/snapshot/snapshot_test.go

@@ -214,7 +214,7 @@ func TestSnapshotFiles(t *testing.T) {
 	filesToSnapshot := []string{
 		filepath.Join(testDir, "foo"),
 	}
-	tarPath, err := snapshotter.TakeSnapshot(filesToSnapshot, false)
+	tarPath, err := snapshotter.TakeSnapshot(filesToSnapshot, false, false)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -361,7 +361,7 @@ func TestSnasphotPreservesFileOrder(t *testing.T) {
 		}
 
 		// Take a snapshot
-		tarPath, err := snapshotter.TakeSnapshot(filesToSnapshot, false)
+		tarPath, err := snapshotter.TakeSnapshot(filesToSnapshot, false, false)
 
 		if err != nil {
 			t.Fatalf("Error taking snapshot of fs: %s", err)
@@ -391,6 +391,46 @@ func TestSnasphotPreservesFileOrder(t *testing.T) {
 	}
 }
 
+func TestSnapshotWithForceBuildMetadataSet(t *testing.T) {
+	_, snapshotter, cleanup, err := setUpTest()
+	defer cleanup()
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	filesToSnapshot := []string{}
+
+	// snapshot should be taken regardless, if forceBuildMetadata flag is set
+	filename, err := snapshotter.TakeSnapshot(filesToSnapshot, false, true)
+	if err != nil {
+		t.Fatalf("Error taking snapshot of fs: %s", err)
+	}
+	if filename == "" {
+		t.Fatalf("Filename returned from snapshot is empty.")
+	}
+}
+
+func TestSnapshotWithForceBuildMetadataIsNotSet(t *testing.T) {
+	_, snapshotter, cleanup, err := setUpTest()
+	defer cleanup()
+
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	filesToSnapshot := []string{}
+
+	// snapshot should not be taken
+	filename, err := snapshotter.TakeSnapshot(filesToSnapshot, false, false)
+	if err != nil {
+		t.Fatalf("Error taking snapshot of fs: %s", err)
+	}
+	if filename != "" {
+		t.Fatalf("Filename returned is expected to be empty.")
+	}
+}
+
 func TestSnasphotPreservesWhiteoutOrder(t *testing.T) {
 	newFiles := map[string]string{
 		"foo":     "newbaz1",
@@ -430,7 +470,7 @@ func TestSnasphotPreservesWhiteoutOrder(t *testing.T) {
 		}
 
 		// Take a snapshot
-		_, err = snapshotter.TakeSnapshot(filesToSnapshot, false)
+		_, err = snapshotter.TakeSnapshot(filesToSnapshot, false, false)
 		if err != nil {
 			t.Fatalf("Error taking snapshot of fs: %s", err)
 		}
@@ -444,7 +484,7 @@ func TestSnasphotPreservesWhiteoutOrder(t *testing.T) {
 		}
 
 		// Take a snapshot again
-		tarPath, err := snapshotter.TakeSnapshot(filesToSnapshot, true)
+		tarPath, err := snapshotter.TakeSnapshot(filesToSnapshot, true, false)
 		if err != nil {
 			t.Fatalf("Error taking snapshot of fs: %s", err)
 		}