Using xtrabackup-v2 as SST method in MariaDB Galera cluster I have configured mariadb galera cluster as docker swarm service using official docker image:
during cluster startup rsync (default SST method) works fine.
Wanted to change it to xtrabackup or xtrabackup-v2, so used the following configuration in my.cnf according to docs:

[mysqld]
wsrep_sst_auth = &lt;wsrep_sst_user&gt;:&lt;password&gt;
wsrep_sst_method = xtrabackup-v2 (or xtrabackup)
datadir = /var/lib/mysql/

[client]
socket =/var/run/mysqld/mysqld.sock


donor server starts fine, but getting the errors below during joiner server startup:


  2018-05-07 13:08:26 139750451541760 [Warning] WSREP: Gap in state sequence. Need state transfer.
  2018-05-07 13:08:26 139750232831744 [Note] WSREP: Running: 'wsrep_sst_xtrabackup-v2 --role 'joiner' --address '10.0.0.37' --datadir '/var/lib/mysql/'   --parent '108'  '' '
  WSREP_SST: [INFO] Logging all stderr of SST/Innobackupex to syslog (20180507 13:08:26.937)
  
  2018-05-07 13:08:29 139750249850624 [Note] WSREP: (fdead878, 'tcp://0.0.0.0:4567') turning message relay requesting off
  
  2018-05-07 13:10:07 139750232831744 [ERROR] WSREP: Failed to read 'ready ' from: wsrep_sst_xtrabackup-v2 --role 'joiner' --address '10.0.0.37' --datadir '/var/lib/mysql/'   --parent '108'  ''
          Read: '(null)'
  
  2018-05-07 13:10:07 139750232831744 [ERROR] WSREP: Process completed with error: wsrep_sst_xtrabackup-v2 --role 'joiner' --address '10.0.0.37' --datadir '/var/lib/mysql/'   --parent '108'  '' : 32 (Broken pipe)
  
  2018-05-07 13:10:07 139750451541760 [ERROR] WSREP: Failed to prepare for 'xtrabackup-v2' SST. Unrecoverable.
  2018-05-07 13:10:07 139750451541760 [ERROR] Aborting
  
  Error in my_thread_global_end(): 1 threads didn't exit


Other wsrep values:

wsrep_on=ON 
wsrep_provider=/usr/lib/libgalera_smm.so 
wsrep_cluster_address=gcomm:// (for first node to start, and virtual_ip of the first node on 2 other nodes)


How to configure xtrabackup as SST method in MariaDB correctly?
The two scripts (or maybe just the last one, but you need both) /usr/bin/wsrep_sst_common and /usr/bin/wsrep_sst_xtrabackup-v2 are broken in 10.2.13, but you can get fixed versions from bug ticket MDEV-15254.