Xtrabackup package not working
The main xtrabackup file is missing.
And, right now, the package is useless.
More details here:
https://forum.alpinelinux.org/forum/general-discussion/xtrabackup-package-missing-binary-xtrabackup55
(from redmine: issue id 6533, created on 2016-12-15, closed on 2016-12-22)