nodeup file: Set owner & group when we write the file.

Otherwise we had an issue where the file existed with the correct
owner/group; when we rewrote it we set the owner/group to root/root;
but we then didn't set the owner/group if they were previously
correct.

Was visible in the flatcar test results.

upup/pkg/fi/files.go

@@ -29,7 +29,8 @@ import (
 	"k8s.io/kops/util/pkg/hashing"
 )
 
-func WriteFile(destPath string, contents Resource, fileMode os.FileMode, dirMode os.FileMode) error {
+// WriteFile writes a file to the specified path, setting the mode, owner & group.
+func WriteFile(destPath string, contents Resource, fileMode os.FileMode, dirMode os.FileMode, owner string, group string) error {
 	err := os.MkdirAll(path.Dir(destPath), dirMode)
 	if err != nil {
 		return fmt.Errorf("error creating directories for destination file %q: %v", destPath, err)
@@ -45,6 +46,11 @@ func WriteFile(destPath string, contents Resource, fileMode os.FileMode, dirMode
 		return err
 	}
 
+	_, err = EnsureFileOwner(destPath, owner, group)
+	if err != nil {
+		return err
+	}
+
 	return nil
 }
 

upup/pkg/fi/files_owner.go

@@ -26,6 +26,8 @@ import (
 	"k8s.io/klog/v2"
 )
 
+// EnsureFileOwner will set the owner & group for a file.
+// Empty values for owner/group will leave the owner/group unchanged.
 func EnsureFileOwner(destPath string, owner string, groupName string) (bool, error) {
 	changed := false
 	stat, err := os.Lstat(destPath)

upup/pkg/fi/nodeup/nodetasks/file.go

@@ -234,7 +234,7 @@ func (_ *File) RenderLocal(t *local.LocalTarget, a, e, changes *File) error {
 		}
 	} else if e.Type == FileType_File {
 		if changes.Contents != nil {
-			err = fi.WriteFile(e.Path, e.Contents, fileMode, dirMode)
+			err = fi.WriteFile(e.Path, e.Contents, fileMode, dirMode, fi.StringValue(e.Owner), fi.StringValue(e.Group))
 			if err != nil {
 				return fmt.Errorf("error copying file %q: %v", e.Path, err)
 			}

upup/pkg/fi/nodeup/nodetasks/service.go

@@ -278,7 +278,7 @@ func (_ *Service) RenderLocal(t *local.LocalTarget, a, e, changes *Service) erro
 
 	if changes.Definition != nil {
 		servicePath := path.Join(systemdSystemPath, serviceName)
-		err := fi.WriteFile(servicePath, fi.NewStringResource(*e.Definition), 0644, 0755)
+		err := fi.WriteFile(servicePath, fi.NewStringResource(*e.Definition), 0644, 0755, "", "")
 		if err != nil {
 			return fmt.Errorf("error writing systemd service file: %v", err)
 		}