Add support for S3 custom endpoint

For S3-compatible object storage (like minio),
this patch enable to use custom endpoint-url.

Fix #531

pkg/buildcontext/s3.go

@@ -19,6 +19,7 @@ package buildcontext
 import (
 	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/GoogleContainerTools/kaniko/pkg/constants"
 	"github.com/GoogleContainerTools/kaniko/pkg/util"
@@ -36,9 +37,21 @@ type S3 struct {
 // UnpackTarFromBuildContext download and untar a file from s3
 func (s *S3) UnpackTarFromBuildContext() (string, error) {
 	bucket, item := util.GetBucketAndItem(s.context)
-	sess, err := session.NewSessionWithOptions(session.Options{
+	option := session.Options{
 		SharedConfigState: session.SharedConfigEnable,
-	})
+	}
+	endpoint := os.Getenv(constants.S3EndpointEnv)
+	forcePath := false
+	if strings.ToLower(os.Getenv(constants.S3ForcePathStyle)) == "true" {
+		forcePath = true
+	}
+	if endpoint != "" {
+		option.Config = aws.Config{
+			Endpoint: aws.String(endpoint),
+			S3ForcePathStyle: aws.Bool(forcePath),
+		}
+	}
+	sess, err := session.NewSessionWithOptions(option)
 	if err != nil {
 		return bucket, err
 	}

pkg/constants/constants.go

@@ -70,6 +70,10 @@ const (
 
 	// Name of the .dockerignore file
 	Dockerignore = ".dockerignore"
+
+	// S3 Custom endpoint ENV name
+	S3EndpointEnv = "S3_ENDPOINT"
+	S3ForcePathStyle = "S3_FORCE_PATH_STYLE"
 )
 
 // ScratchEnvVars are the default environment variables needed for a scratch image.