mz523: skip interstage clean

README.md

@@ -138,6 +138,7 @@ expect - see [Known Issues](#known-issues).
       - [Flag `FF_KANIKO_OCI_WARMER`](#flag-ff_kaniko_oci_warmer)
       - [Flag `FF_KANIKO_RUN_VIA_TINI`](#flag-ff_kaniko_run_via_tini)
       - [Flag `FF_KANIKO_COPY_CHMOD_ON_IMPLICIT_DIRS`](#flag-ff_kaniko_copy_chmod_on_implicit_dirs)
+      - [Flag `FF_KANIKO_SKIP_INTERSTAGE_CLEANUP`](#flag-ff_kaniko_skip_interstage_cleanup)
     - [Debug Image](#debug-image)
   - [Security](#security)
     - [Verifying Signed Kaniko Images](#verifying-signed-kaniko-images)
@@ -1429,6 +1430,12 @@ When files are copied into a non-existing directory, both kaniko and buildkit wi
 Set this flag to `true` to implement COPY chmod like buildkit. Defaults to `false`.
 Currently no plans to activate.
 
+#### Flag `FF_KANIKO_SKIP_INTERSTAGE_CLEANUP`
+
+In multi-stage builds, kaniko always tears down the filesystem and re-unpacks the base image between stages. When a stage's `FROM` resolves to the immediately preceding preceding stage, this round-trip is redundant.
+Set this flag to `true` to skip cleanup when consecutive stages chain directly Defaults to `false`.
+
+
 ### Debug Image
 
 The kaniko executor image is based on scratch and doesn't contain a shell. We

golden/golden_test.go

@@ -30,6 +30,7 @@ import (
 	testissuemz195 "github.com/osscontainertools/kaniko/golden/testdata/test_issue_mz195"
 	testissuemz333 "github.com/osscontainertools/kaniko/golden/testdata/test_issue_mz333"
 	testissuemz338 "github.com/osscontainertools/kaniko/golden/testdata/test_issue_mz338"
+	testissuemz523 "github.com/osscontainertools/kaniko/golden/testdata/test_issue_mz523"
 	testunittests "github.com/osscontainertools/kaniko/golden/testdata/test_unittests"
 	"github.com/osscontainertools/kaniko/golden/types"
 	"github.com/osscontainertools/kaniko/pkg/config"
@@ -62,6 +63,7 @@ var allTests = map[string][]types.GoldenTests{
 	"test_issue_mz195": {testissuemz195.Tests},
 	"test_issue_mz333": {testissuemz333.Tests},
 	"test_issue_mz338": {testissuemz338.Tests},
+	"test_issue_mz523": {testissuemz523.Tests},
 	"test_unittests":   testunittests.Tests,
 }
 var update bool

golden/testdata/test_issue_mz523/Dockerfile

@@ -0,0 +1,15 @@
+FROM debian:12.10 AS first-stage
+
+# mz523: We can't squash second+first stages,
+# but when we switch the context we don't need
+# to clean the filesystem and unpack the image again.
+
+FROM first-stage AS second-stage
+RUN touch test
+
+FROM second-stage AS third-stage
+RUN touch test2
+
+FROM first-stage AS fourth-stage
+COPY --from=second-stage test test
+COPY --from=third-stage test2 test2

golden/testdata/test_issue_mz523/plans/nocleanup

@@ -0,0 +1,18 @@
+FROM debian:12.10 AS first-stage
+UNPACK debian:12.10
+SAVE STAGE /kaniko/stages/0
+
+FROM first-stage AS second-stage
+RUN touch test
+SAVE STAGE /kaniko/stages/1
+SAVE FILES [test] /kaniko/deps/1
+
+FROM second-stage AS third-stage
+RUN touch test2
+SAVE FILES [test2] /kaniko/deps/2
+CLEAN
+
+FROM first-stage AS fourth-stage
+UNPACK /kaniko/stages/0
+COPY --from=second-stage test test
+COPY --from=third-stage test2 test2

golden/testdata/test_issue_mz523/plans/normal

@@ -0,0 +1,22 @@
+FROM debian:12.10 AS first-stage
+UNPACK debian:12.10
+SAVE STAGE /kaniko/stages/0
+CLEAN
+
+FROM first-stage AS second-stage
+UNPACK /kaniko/stages/0
+RUN touch test
+SAVE STAGE /kaniko/stages/1
+SAVE FILES [test] /kaniko/deps/1
+CLEAN
+
+FROM second-stage AS third-stage
+UNPACK /kaniko/stages/1
+RUN touch test2
+SAVE FILES [test2] /kaniko/deps/2
+CLEAN
+
+FROM first-stage AS fourth-stage
+UNPACK /kaniko/stages/0
+COPY --from=second-stage test test
+COPY --from=third-stage test2 test2

golden/testdata/test_issue_mz523/test.go

@@ -0,0 +1,21 @@
+package testissuemz523
+
+import "github.com/osscontainertools/kaniko/golden/types"
+
+var Tests = types.GoldenTests{
+	Name:       "test_issue_mz523",
+	Dockerfile: "Dockerfile",
+	Tests: []types.GoldenTest{
+		{
+			Args: []string{"--no-push"},
+			Plan: "normal",
+		},
+		{
+			Args: []string{"--no-push"},
+			Env: map[string]string{
+				"FF_KANIKO_SKIP_INTERSTAGE_CLEANUP": "1",
+			},
+			Plan: "nocleanup",
+		},
+	},
+}

integration/images.go

@@ -94,6 +94,7 @@ var KanikoEnv = []string{
 	"FF_KANIKO_OCI_WARMER=1",
 	"FF_KANIKO_RUN_VIA_TINI=1",
 	"FF_KANIKO_COPY_CHMOD_ON_IMPLICIT_DIRS=1",
+	"FF_KANIKO_SKIP_INTERSTAGE_CLEANUP=1",
 }
 
 var WarmerEnv = []string{

pkg/config/stage.go

@@ -31,4 +31,6 @@ type KanikoStage struct {
 	SaveStage              bool
 	MetaArgs               []instructions.ArgCommand
 	Index                  int
+	Unpack                 bool
+	Clean                  bool
 }

pkg/dockerfile/dockerfile.go

@@ -355,6 +355,8 @@ func MakeKanikoStages(opts *config.KanikoOptions, stages []instructions.Stage, m
 			Final:                  i == targetStage,
 			MetaArgs:               metaArgs,
 			Index:                  i,
+			Unpack:                 true,
+			Clean:                  true,
 		}
 	}
 	if opts.SkipUnusedStages && config.EnvBoolDefault("FF_KANIKO_SQUASH_STAGES", true) {
@@ -383,6 +385,14 @@ func MakeKanikoStages(opts *config.KanikoOptions, stages []instructions.Stage, m
 		}
 		kanikoStages = onlyUsedStages
 	}
+	if config.EnvBool("FF_KANIKO_SKIP_INTERSTAGE_CLEANUP") {
+		for i := range kanikoStages {
+			if i > 0 && kanikoStages[i].BaseImageIndex == kanikoStages[i-1].Index {
+				kanikoStages[i-1].Clean = false
+				kanikoStages[i].Unpack = false
+			}
+		}
+	}
 	return kanikoStages, nil
 }
 
@@ -459,5 +469,7 @@ func squash(a, b config.KanikoStage) config.KanikoStage {
 		SaveStage:              b.SaveStage,
 		MetaArgs:               append(a.MetaArgs, b.MetaArgs...),
 		Index:                  b.Index,
+		Unpack:                 a.Unpack,
+		Clean:                  b.Clean,
 	}
 }

pkg/executor/build.go

@@ -69,6 +69,8 @@ type snapShotter interface {
 type stageBuilder struct {
 	index            int
 	final            bool
+	unpack           bool
+	clean            bool
 	image            v1.Image
 	cf               *v1.ConfigFile
 	baseImageDigest  string
@@ -142,6 +144,8 @@ func newStageBuilder(args *dockerfile.BuildArgs, opts *config.KanikoOptions, sta
 	s := &stageBuilder{
 		index:            stage.Index,
 		final:            stage.Final,
+		unpack:           stage.Unpack,
+		clean:            stage.Clean,
 		image:            sourceImage,
 		cf:               imageConfig,
 		snapshotter:      snapshotter,
@@ -339,7 +343,7 @@ func (s *stageBuilder) build(digestToCacheKey map[string]string) error {
 	if s.final && s.opts.Materialize {
 		shouldUnpack = true
 	}
-	if s.index == 0 && s.opts.InitialFSUnpacked {
+	if s.index == 0 && s.opts.InitialFSUnpacked || !s.unpack {
 		shouldUnpack = false
 	}
 
@@ -751,10 +755,12 @@ func RenderStages(stages []config.KanikoStage, opts *config.KanikoOptions, fileC
 		} else {
 			printf("FROM %s\n", s.BaseName)
 		}
-		if s.BaseImageStoredLocally {
-			printf("UNPACK %s%d\n", config.KanikoIntermediateStagesDir, s.BaseImageIndex)
-		} else {
-			printf("UNPACK %s\n", s.BaseName)
+		if s.Unpack {
+			if s.BaseImageStoredLocally {
+				printf("UNPACK %s%d\n", config.KanikoIntermediateStagesDir, s.BaseImageIndex)
+			} else {
+				printf("UNPACK %s\n", s.BaseName)
+			}
 		}
 		for _, c := range s.Commands {
 			command, err := commands.GetCommand(c, fileContext, opts.Secrets, opts.RunV2, opts.CacheCopyLayers, opts.CacheRunLayers)
@@ -782,9 +788,13 @@ func RenderStages(stages []config.KanikoStage, opts *config.KanikoOptions, fileC
 		if len(filesToSave) > 0 {
 			printf("SAVE FILES %v %s%d\n", filesToSave, config.KanikoInterStageDepsDir, s.Index)
 		}
-		printf("CLEAN\n\n")
-		if opts.PreserveContext && !opts.PreCleanup {
-			printf("RESTORE CONTEXT\n\n")
+		if s.Clean {
+			printf("CLEAN\n\n")
+			if opts.PreserveContext && !opts.PreCleanup {
+				printf("RESTORE CONTEXT\n\n")
+			}
+		} else {
+			printf("\n")
 		}
 	}
 	logrus.Panic("unreachable - we should always have a final stage")
@@ -978,18 +988,20 @@ func DoBuild(opts *config.KanikoOptions) (image v1.Image, retErr error) {
 		}
 
 		// Delete the filesystem
-		if err := util.DeleteFilesystem(); err != nil {
-			return nil, fmt.Errorf("deleting file system after stage %d: %w", stage.Index, err)
-		}
-		if opts.PreserveContext && !opts.PreCleanup {
-			if tarball == "" {
-				return nil, fmt.Errorf("context snapshot is missing")
+		if sb.clean {
+			if err := util.DeleteFilesystem(); err != nil {
+				return nil, fmt.Errorf("deleting file system after stage %d: %w", stage.Index, err)
 			}
-			_, err := util.UnpackLocalTarArchive(tarball, config.RootDir)
-			if err != nil {
-				return nil, fmt.Errorf("failed to unpack context snapshot: %w", err)
+			if opts.PreserveContext && !opts.PreCleanup {
+				if tarball == "" {
+					return nil, fmt.Errorf("context snapshot is missing")
+				}
+				_, err := util.UnpackLocalTarArchive(tarball, config.RootDir)
+				if err != nil {
+					return nil, fmt.Errorf("failed to unpack context snapshot: %w", err)
+				}
+				logrus.Info("Context restored")
 			}
-			logrus.Info("Context restored")
 		}
 	}