Add a new flag to cleanup the filesystem at the end

Currently, kaniko can only build a single image per container run, because the filesystem is full of the content of the first image.
When running kaniko in Jenkins, where we need to start the container "doing nothing" first (using the debug kaniko container), and then exec /kaniko/executor, this is a limitation because it means that if we want to build multiple images, we need to start multiple containers - see https://groups.google.com/forum/#!topic/kaniko-users/_7LivHdMdy0 for more details

A solution to fix this issue is to add a new flag to cleanup the filesystem at the end - the same way it is done between stages when building a multi-stages image. This way, the same (debug) container can be used to build multiple images.

README.md

@@ -317,6 +317,10 @@ If `--destination=gcr.io/kaniko-project/test`, then cached layers will be stored
 
 _This flag must be used in conjunction with the `--cache=true` flag._
 
+#### --cleanup
+
+Set this flag to cleanup the filesystem at the end, leaving a clean kaniko container (if you want to build multiple images in the same container, using the debug kaniko image)
+
 ### Debug Image
 
 The kaniko executor image is based off of scratch and doesn't contain a shell.

cmd/executor/cmd/root.go

@@ -37,11 +37,13 @@ var (
 	opts     = &config.KanikoOptions{}
 	logLevel string
 	force    bool
+	cleanup  bool
 )
 
 func init() {
 	RootCmd.PersistentFlags().StringVarP(&logLevel, "verbosity", "v", constants.DefaultLogLevel, "Log level (debug, info, warn, error, fatal, panic")
 	RootCmd.PersistentFlags().BoolVarP(&force, "force", "", false, "Force building outside of a container")
+	RootCmd.PersistentFlags().BoolVarP(&cleanup, "cleanup", "", false, "Clean the filesystem at the end")
 	addKanikoOptionsFlags(RootCmd)
 	addHiddenFlags(RootCmd)
 }
@@ -77,6 +79,11 @@ var RootCmd = &cobra.Command{
 		if err := executor.DoPush(image, opts); err != nil {
 			exit(errors.Wrap(err, "error pushing image"))
 		}
+		if cleanup {
+			if err := util.DeleteFilesystem(); err != nil {
+				exit(errors.Wrap(err, "error cleaning filesystem"))
+			}
+		}
 	},
 }