Make the Digest calculation faster for locally-cached images. (#534)

Right now when we find a v1.Tarball in the local disk cache, we
recompute the digest. This is very expensive and redundant, because
we store tarballs by their digest and use that as a key to look them up.

pkg/cache/cache.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"os"
 	"path"
+	"path/filepath"
 	"time"
 
 	"github.com/GoogleContainerTools/kaniko/pkg/config"
@@ -114,11 +115,31 @@ func LocalSource(opts *config.KanikoOptions, cacheKey string) (v1.Image, error)
 		return nil, nil
 	}
 
-	imgTar, err := tarball.ImageFromPath(path, nil)
+	logrus.Infof("Found %s in local cache", cacheKey)
+	return cachedImageFromPath(path)
+}
+
+// cachedImage represents a v1.Tarball that is cached locally in a CAS.
+// Computing the digest for a v1.Tarball is very expensive. If the tarball
+// is named with the digest we can store this and return it directly rather
+// than recompute it.
+type cachedImage struct {
+	digest string
+	v1.Image
+}
+
+func (c *cachedImage) Digest() (v1.Hash, error) {
+	return v1.NewHash(c.digest)
+}
+
+func cachedImageFromPath(p string) (v1.Image, error) {
+	imgTar, err := tarball.ImageFromPath(p, nil)
 	if err != nil {
 		return nil, errors.Wrap(err, "getting image from path")
 	}
 
-	logrus.Infof("Found %s in local cache", cacheKey)
-	return imgTar, nil
+	return &cachedImage{
+		digest: filepath.Base(p),
+		Image:  imgTar,
+	}, nil
 }

pkg/executor/build.go

@@ -23,12 +23,15 @@ import (
 	"strconv"
 	"time"
 
+	"github.com/google/go-containerregistry/pkg/v1/partial"
+
 	"github.com/moby/buildkit/frontend/dockerfile/instructions"
 
 	"golang.org/x/sync/errgroup"
 
 	"github.com/google/go-containerregistry/pkg/name"
 	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"github.com/google/go-containerregistry/pkg/v1/empty"
 	"github.com/google/go-containerregistry/pkg/v1/mutate"
 	"github.com/google/go-containerregistry/pkg/v1/tarball"
 	"github.com/pkg/errors"
@@ -59,21 +62,20 @@ type stageBuilder struct {
 
 // newStageBuilder returns a new type stageBuilder which contains all the information required to build the stage
 func newStageBuilder(opts *config.KanikoOptions, stage config.KanikoStage) (*stageBuilder, error) {
-	t := timing.Start("Retrieving Source Image")
 	sourceImage, err := util.RetrieveSourceImage(stage, opts)
 	if err != nil {
 		return nil, err
 	}
-	timing.DefaultRun.Stop(t)
-	t = timing.Start("Retrieving Config File")
-	imageConfig, err := util.RetrieveConfigFile(sourceImage)
+
+	imageConfig, err := initializeConfig(sourceImage)
 	if err != nil {
 		return nil, err
 	}
-	timing.DefaultRun.Stop(t)
+
 	if err := resolveOnBuild(&stage, &imageConfig.Config); err != nil {
 		return nil, err
 	}
+
 	hasher, err := getHasher(opts.SnapshotMode)
 	if err != nil {
 		return nil, err
@@ -95,6 +97,18 @@ func newStageBuilder(opts *config.KanikoOptions, stage config.KanikoStage) (*sta
 	}, nil
 }
 
+func initializeConfig(img partial.WithConfigFile) (*v1.ConfigFile, error) {
+	imageConfig, err := img.ConfigFile()
+	if err != nil {
+		return nil, err
+	}
+
+	if img == empty.Image {
+		imageConfig.Config.Env = constants.ScratchEnvVars
+	}
+	return imageConfig, nil
+}
+
 func (s *stageBuilder) optimize(compositeKey CompositeCache, cfg v1.Config, cmds []commands.DockerCommand, args *dockerfile.BuildArgs) error {
 	if !s.opts.Cache {
 		return nil
@@ -429,7 +443,7 @@ func fetchExtraStages(stages []config.KanikoStage, opts *config.KanikoOptions) e
 			}
 			// This must be an image name, fetch it.
 			logrus.Debugf("Found extra base image stage %s", c.From)
-			sourceImage, err := util.RetrieveRemoteImage(c.From, opts, false)
+			sourceImage, err := util.RetrieveRemoteImage(c.From, opts)
 			if err != nil {
 				return err
 			}

pkg/util/image_util.go

@@ -23,12 +23,13 @@ import (
 	"path/filepath"
 	"strconv"
 
+	"github.com/GoogleContainerTools/kaniko/pkg/timing"
+
 	"github.com/GoogleContainerTools/kaniko/pkg/creds"
 
 	"github.com/google/go-containerregistry/pkg/name"
 	"github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/empty"
-	"github.com/google/go-containerregistry/pkg/v1/partial"
 	"github.com/google/go-containerregistry/pkg/v1/remote"
 	"github.com/google/go-containerregistry/pkg/v1/tarball"
 	"github.com/sirupsen/logrus"
@@ -46,6 +47,8 @@ var (
 
 // RetrieveSourceImage returns the base image of the stage at index
 func RetrieveSourceImage(stage config.KanikoStage, opts *config.KanikoOptions) (v1.Image, error) {
+	t := timing.Start("Retrieving Source Image")
+	defer timing.DefaultRun.Stop(t)
 	buildArgs := opts.BuildArgs
 	var metaArgsString []string
 	for _, arg := range stage.MetaArgs {
@@ -67,20 +70,21 @@ func RetrieveSourceImage(stage config.KanikoStage, opts *config.KanikoOptions) (
 		return retrieveTarImage(stage.BaseImageIndex)
 	}
 
-	// Otherwise, initialize image as usual
-	return RetrieveRemoteImage(currentBaseName, opts, false)
-}
+	// Finally, check if local caching is enabled
+	// If so, look in the local cache before trying the remote registry
+	if opts.Cache && opts.CacheDir != "" {
+		cachedImage, err := cachedImage(opts, currentBaseName)
+		if cachedImage != nil {
+			return cachedImage, nil
+		}
 
-// RetrieveConfigFile returns the config file for an image
-func RetrieveConfigFile(sourceImage partial.WithConfigFile) (*v1.ConfigFile, error) {
-	imageConfig, err := sourceImage.ConfigFile()
-	if err != nil {
-		return nil, err
+		if err != nil {
+			logrus.Infof("Error while retrieving image from cache: %v", err)
+		}
 	}
-	if sourceImage == empty.Image {
-		imageConfig.Config.Env = constants.ScratchEnvVars
-	}
-	return imageConfig, nil
+
+	// Otherwise, initialize image as usual
+	return RetrieveRemoteImage(currentBaseName, opts)
 }
 
 func tarballImage(index int) (v1.Image, error) {
@@ -89,20 +93,8 @@ func tarballImage(index int) (v1.Image, error) {
 	return tarball.ImageFromPath(tarPath, nil)
 }
 
-func remoteImage(image string, opts *config.KanikoOptions, forceNoCache bool) (v1.Image, error) {
+func remoteImage(image string, opts *config.KanikoOptions) (v1.Image, error) {
 	logrus.Infof("Downloading base image %s", image)
-	// First, check if local caching is enabled
-	// If so, look in the local cache before trying the remote registry
-	if opts.Cache && opts.CacheDir != "" && !forceNoCache {
-		cachedImage, err := cachedImage(opts, image)
-		if cachedImage != nil {
-			return cachedImage, nil
-		}
-
-		if err != nil {
-			logrus.Warnf("Error while retrieving image from cache: %v", err)
-		}
-	}
 	ref, err := name.ParseReference(image, name.WeakValidation)
 	if err != nil {
 		return nil, err
@@ -143,7 +135,7 @@ func cachedImage(opts *config.KanikoOptions, image string) (v1.Image, error) {
 	if d, ok := ref.(name.Digest); ok {
 		cacheKey = d.DigestStr()
 	} else {
-		img, err := remoteImage(image, opts, true)
+		img, err := remoteImage(image, opts)
 		if err != nil {
 			return nil, err
 		}

pkg/util/image_util_test.go

@@ -51,7 +51,7 @@ func Test_StandardImage(t *testing.T) {
 	defer func() {
 		RetrieveRemoteImage = original
 	}()
-	mock := func(image string, opts *config.KanikoOptions, forceNoCache bool) (v1.Image, error) {
+	mock := func(image string, opts *config.KanikoOptions) (v1.Image, error) {
 		return nil, nil
 	}
 	RetrieveRemoteImage = mock