Add backup-version file in backup tarball

Signed-off-by: Wayne Witzel III <wayne@riotousliving.com>

changelogs/unreleased/1117-wwitzel3

@@ -0,0 +1 @@
+Add backup-version file in backup tarball.

pkg/backup/backup.go

@@ -22,6 +22,7 @@ import (
 	"context"
 	"fmt"
 	"io"
+	"strconv"
 	"time"
 
 	"github.com/pkg/errors"
@@ -41,6 +42,9 @@ import (
 	kubeutil "github.com/heptio/ark/pkg/util/kube"
 )
 
+// BackupVersion is the current backup version for Ark.
+const BackupVersion = 1
+
 // Backupper performs backups.
 type Backupper interface {
 	// Backup takes a backup using the specification in the api.Backup and writes backup and log data
@@ -221,6 +225,10 @@ func (kb *kubernetesBackupper) Backup(logger logrus.FieldLogger, backupRequest *
 	log := logger.WithField("backup", kubeutil.NamespaceAndName(backupRequest))
 	log.Info("Starting backup")
 
+	if err := kb.writeBackupVersion(tw); err != nil {
+		return errors.WithStack(err)
+	}
+
 	backupRequest.NamespaceIncludesExcludes = getNamespaceIncludesExcludes(backupRequest.Backup)
 	log.Infof("Including namespaces: %s", backupRequest.NamespaceIncludesExcludes.IncludesString())
 	log.Infof("Excluding namespaces: %s", backupRequest.NamespaceIncludesExcludes.ExcludesString())
@@ -292,6 +300,25 @@ func (kb *kubernetesBackupper) Backup(logger logrus.FieldLogger, backupRequest *
 	return err
 }
 
+func (kb *kubernetesBackupper) writeBackupVersion(tw *tar.Writer) error {
+	versionString := strconv.Itoa(BackupVersion)
+
+	hdr := &tar.Header{
+		Name:     "backup-version",
+		Size:     int64(len(versionString)),
+		Typeflag: tar.TypeReg,
+		Mode:     0644,
+		ModTime:  time.Now(),
+	}
+	if err := tw.WriteHeader(hdr); err != nil {
+		return err
+	}
+	if _, err := tw.Write([]byte(versionString)); err != nil {
+		return err
+	}
+	return nil
+}
+
 type tarWriter interface {
 	io.Closer
 	Write([]byte) (int, error)

pkg/controller/backup_controller.go

@@ -51,8 +51,6 @@ import (
 	"github.com/heptio/ark/pkg/volume"
 )
 
-const backupVersion = 1
-
 type backupController struct {
 	*genericController
 
@@ -245,7 +243,7 @@ func (c *backupController) prepareBackupRequest(backup *api.Backup) *pkgbackup.R
 	}
 
 	// set backup version
-	request.Status.Version = backupVersion
+	request.Status.Version = pkgbackup.BackupVersion
 
 	// calculate expiration
 	if request.Spec.TTL.Duration > 0 {