Add support for zstd compression (GoogleContainerTools#2313)

* Add support for configurable compression algorithm (gzip, zstd) and compression level

We want to make the layer compression in kaniko configurable, so we have added two optional command line arguments “--compression” and “--compression-level”. The former allows the user to specify a compression algorithm (zstd, gzip) and the latter can be used to specify the compression level.

Depending on the selected compression algorithm and level we modify the set of layerOptions that are used to create tarball layers in `push.go` and `build.go`.

The actual implementation of the zstd support can be found in our fork of the go-containerregistry package for which we have filed this PR: google/go-containerregistry#1487

The changes should be fully backwards compatible.

* Restrict inputs for compression flag to gzip and zstd

This change will ensure that users can only specify supported compression algorithms (`zstd`, `gzip`) to the `--compression` flag.

* Fix incorrect type for switch statements on config.Compression

cmd/executor/cmd/root.go

@@ -225,6 +225,8 @@ func addKanikoOptionsFlags() {
 	RootCmd.PersistentFlags().StringVarP(&opts.ImageNameDigestFile, "image-name-with-digest-file", "", "", "Specify a file to save the image name w/ digest of the built image to.")
 	RootCmd.PersistentFlags().StringVarP(&opts.ImageNameTagDigestFile, "image-name-tag-with-digest-file", "", "", "Specify a file to save the image name w/ image tag w/ digest of the built image to.")
 	RootCmd.PersistentFlags().StringVarP(&opts.OCILayoutPath, "oci-layout-path", "", "", "Path to save the OCI image layout of the built image.")
+	RootCmd.PersistentFlags().VarP(&opts.Compression, "compression", "", "Compression algorithm (gzip, zstd)")
+	RootCmd.PersistentFlags().IntVarP(&opts.CompressionLevel, "compression-level", "", -1, "Compression level")
 	RootCmd.PersistentFlags().BoolVarP(&opts.Cache, "cache", "", false, "Use cache when building image")
 	RootCmd.PersistentFlags().BoolVarP(&opts.CompressedCaching, "compressed-caching", "", true, "Compress the cached layers. Decreases build time, but increases memory usage.")
 	RootCmd.PersistentFlags().BoolVarP(&opts.Cleanup, "cleanup", "", false, "Clean the filesystem at the end")

pkg/config/options.go

@@ -69,6 +69,8 @@ type KanikoOptions struct {
 	ImageNameDigestFile      string
 	ImageNameTagDigestFile   string
 	OCILayoutPath            string
+	Compression              Compression
+	CompressionLevel         int
 	ImageFSExtractRetry      int
 	SingleSnapshot           bool
 	Reproducible             bool
@@ -128,6 +130,33 @@ func (k *KanikoGitOptions) Set(s string) error {
 	return nil
 }
 
+// Compression is an enumeration of the supported compression algorithms
+type Compression string
+
+// The collection of known MediaType values.
+const (
+	GZip Compression = "gzip"
+	ZStd Compression = "zstd"
+)
+
+func (c *Compression) String() string {
+	return string(*c)
+}
+
+func (c *Compression) Set(v string) error {
+	switch v {
+	case "gzip", "zstd":
+		*c = Compression(v)
+		return nil
+	default:
+		return errors.New(`must be either "gzip" or "zstd"`)
+	}
+}
+
+func (c *Compression) Type() string {
+	return "compression"
+}
+
 // WarmerOptions are options that are set by command line arguments to the cache warmer.
 type WarmerOptions struct {
 	CacheOptions

pkg/executor/build.go

@@ -518,12 +518,25 @@ func (s *stageBuilder) saveSnapshotToLayer(tarPath string) (v1.Layer, error) {
 		return nil, nil
 	}
 
-	var layer v1.Layer
+	var layerOpts []tarball.LayerOption
+
 	if s.opts.CompressedCaching == true {
-		layer, err = tarball.LayerFromFile(tarPath, tarball.WithCompressedCaching)
-	} else {
-		layer, err = tarball.LayerFromFile(tarPath)
+		layerOpts = append(layerOpts, tarball.WithCompressedCaching)
+	}
+
+	if s.opts.CompressionLevel > 0 {
+		layerOpts = append(layerOpts, tarball.WithCompressionLevel(s.opts.CompressionLevel))
 	}
+
+	switch s.opts.Compression {
+	case config.ZStd:
+		layerOpts = append(layerOpts, tarball.WithCompression("zstd"))
+
+	case config.GZip:
+		// layer already gzipped by default
+	}
+
+	layer, err := tarball.LayerFromFile(tarPath, layerOpts...)
 	if err != nil {
 		return nil, err
 	}

pkg/executor/push.go

@@ -296,16 +296,28 @@ func writeImageOutputs(image v1.Image, destRefs []name.Tag) error {
 // pushLayerToCache pushes layer (tagged with cacheKey) to opts.CacheRepo
 // if opts.CacheRepo doesn't exist, infer the cache from the given destination
 func pushLayerToCache(opts *config.KanikoOptions, cacheKey string, tarPath string, createdBy string) error {
-	var layer v1.Layer
-	var err error
+	var layerOpts []tarball.LayerOption
 	if opts.CompressedCaching == true {
-		layer, err = tarball.LayerFromFile(tarPath, tarball.WithCompressedCaching)
-	} else {
-		layer, err = tarball.LayerFromFile(tarPath)
+		layerOpts = append(layerOpts, tarball.WithCompressedCaching)
 	}
+
+	if opts.CompressionLevel > 0 {
+		layerOpts = append(layerOpts, tarball.WithCompressionLevel(opts.CompressionLevel))
+	}
+
+	switch opts.Compression {
+	case config.ZStd:
+		layerOpts = append(layerOpts, tarball.WithCompression("zstd"))
+
+	case config.GZip:
+		// layer already gzipped by default
+	}
+
+	layer, err := tarball.LayerFromFile(tarPath, layerOpts...)
 	if err != nil {
 		return err
 	}
+
 	cache, err := cache.Destination(opts, cacheKey)
 	if err != nil {
 		return errors.Wrap(err, "getting cache destination")