Persistent volume caching for base images (#383)

* comments

* initial commit for persisent volume caching

* cache warmer works

* general cleanup

* adding some debugging

* adding missing files

* Fixing up cache retrieval and cleanup

* fix tests

* removing auth since we only cache public images

* simplifying the caching logic

* fixing logic

* adding volume cache to integration tests. remove auth from cache warmer image.

* add building warmer to integration-test

* move sample yaml files to examples dir

* small test fix

pkg/cache/cache.go

@@ -18,6 +18,7 @@ package cache
 
 import (
 	"fmt"
+	"path"
 
 	"github.com/GoogleContainerTools/kaniko/pkg/config"
 	"github.com/google/go-containerregistry/pkg/authn"
@@ -25,6 +26,7 @@ import (
 	"github.com/google/go-containerregistry/pkg/name"
 	"github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/remote"
+	"github.com/google/go-containerregistry/pkg/v1/tarball"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 )
@@ -68,3 +70,20 @@ func Destination(opts *config.KanikoOptions, cacheKey string) (string, error) {
 	}
 	return fmt.Sprintf("%s:%s", cache, cacheKey), nil
 }
+
+func LocalSource(opts *config.KanikoOptions, cacheKey string) (v1.Image, error) {
+	cache := opts.CacheDir
+	if cache == "" {
+		return nil, nil
+	}
+
+	path := path.Join(cache, cacheKey)
+
+	imgTar, err := tarball.ImageFromPath(path, nil)
+	if err != nil {
+		return nil, errors.Wrap(err, "getting image from path")
+	}
+
+	logrus.Infof("Found %s in local cache", cacheKey)
+	return imgTar, nil
+}