Error while syncing with second node of galera

[FISH]

I am working on configuring the galera cluster (3 node) on centos7.

The bootstrap node is successfully started.

When I do joined from the second node, the donor is not syncing.

Im getting the below error on 2nd server [joiner]

[root@lab2 mysql]# tailf /var/lib/mysql/mlab2.err
2017-12-07  9:22:28 140434131121920 [Note] WSREP: (0c337321, 'tcp://0.0.0.0:4567') turning message relay requesting off
WSREP_SST: [ERROR] xtrabackup_checkpoints missing, failed innobackupex/SST on donor (20171207 09:22:37.682)
WSREP_SST: [ERROR] Cleanup after exit with status:2 (20171207 09:22:37.685)
2017-12-07  9:22:37 140434093373184 [ERROR] WSREP: Process completed with error: wsrep_sst_xtrabackup-v2 --role 'joiner' --address '10.16.230.173' --datadir '/var/lib/mysql/'   --parent '10549' --binlog 'mysql-bin' : 2 (No such file or directory)
2017-12-07  9:22:37 140434093373184 [ERROR] WSREP: Failed to read uuid:seqno and wsrep_gtid_domain_id from joiner script.
2017-12-07  9:22:37 140434434906368 [ERROR] WSREP: SST failed: 2 (No such file or directory)
2017-12-07  9:22:37 140434434906368 [ERROR] Aborting

2017-12-07  9:22:37 140434122729216 [Warning] WSREP: 1.0 (lab1): State transfer to 0.0 (lab2) failed: -22 (Invalid argument)
2017-12-07  9:22:37 140434122729216 [ERROR] WSREP: gcs/src/gcs_group.cpp:gcs_group_handle_join_msg():736: Will never receive state. Need to abort.
^C

[root@lab2 mysql]# xtrabackup -v
xtrabackup version 2.3.10 based on MySQL server 5.6.24 Linux (x86_64) (revision id: bd0d4403f36)
[root@lab2 mysql]#

ERROR LOG FROM DONOR:

WSREP_SST: [INFO] Sleeping before data transfer for SST (20171207 14:56:25.421)
2017-12-07 14:56:26 140671801358080 [Note] WSREP: (6bff7f82, 'tcp://0.0.0.0:4567') turning message relay requesting off
WSREP_SST: [INFO] Streaming the backup to joiner at 10.16.230.173 4444 (20171207 14:56:35.428)
WSREP_SST: [INFO] Evaluating innobackupex   --no-version-check  $tmpopts $INNOEXTRA --galera-info --stream=$sfmt $itmpdir
 2>${DATA}/innobackup.backup.log | socat -u stdio TCP:10.16.230.173:4444; RC=( ${PIPESTATUS[@]} ) (20171207 14:56:35.436)
WSREP_SST: [ERROR] innobackupex finished with error: 1.  Check /var/lib/mysql//innobackup.backup.log (20171207 14:56:35.4
60)
WSREP_SST: [ERROR] Cleanup after exit with status:22 (20171207 14:56:35.464)
WSREP_SST: [INFO] Cleaning up temporary directories (20171207 14:56:35.469)
2017-12-07 14:56:35 140670274230016 [ERROR] WSREP: Failed to read from: wsrep_sst_xtrabackup-v2 --role 'donor' --address
'10.16.230.173:4444/xtrabackup_sst//1' --socket '/var/lib/mysql/mysql.sock' --datadir '/var/lib/mysql/'     '' --gtid '97
6baded-db75-11e7-9dc0-eb8f39d3e04d:7' --gtid-domain-id '0'
2017-12-07 14:56:35 140670274230016 [ERROR] WSREP: Process completed with error: wsrep_sst_xtrabackup-v2 --role 'donor' -
-address '10.16.230.173:4444/xtrabackup_sst//1' --socket '/var/lib/mysql/mysql.sock' --datadir '/var/lib/mysql/'     '' -
-gtid '976baded-db75-11e7-9dc0-eb8f39d3e04d:7' --gtid-domain-id '0': 22 (Invalid argument)
2017-12-07 14:56:35 140670274230016 [ERROR] WSREP: Command did not run: wsrep_sst_xtrabackup-v2 --role 'donor' --address
'10.16.230.173:4444/xtrabackup_sst//1' --socket '/var/lib/mysql/mysql.sock' --datadir '/var/lib/mysql/'     '' --gtid '97
6baded-db75-11e7-9dc0-eb8f39d3e04d:7' --gtid-domain-id '0'
2017-12-07 14:56:35 140671792965376 [Warning] WSREP: 0.0 (lab1): State transfer to 1.0 (lab2) failed: -22 (Invalid argume
nt)

error log from innobackupex. But the user I provided is ‘backup’:backup as password.

[root@lab1 .ssh]# cat /var/lib/mysql//innobackup.backup.log
171207 14:57:30 innobackupex: Starting the backup operation

IMPORTANT: Please check that the backup run completes successfully.
           At the end of a successful backup run innobackupex
           prints "completed OK!".

171207 14:57:30 Connecting to MySQL server host: localhost, user: not set, password: not set, port: not set, socket: /var/lib/mysql/mysql.sock
Failed to connect to MySQL server: Access denied for user 'mysql'@'localhost' (using password: NO).
[root@lab1 .ssh]#

configuration file:

[root@lab1 .ssh]# cat /etc/my.cnf
[mysqld]
datadir=/var/lib/mysql
log-error=/var/lib/mysql/mariadb-log.err
binlog_format=ROW
default-storage-engine=innodb
innodb_autoinc_lock_mode=2

[galera]
wsrep_on=ON
wsrep_provider=/lib64/galera/libgalera_smm.so
wsrep_cluster_name="test_cluster"
wsrep_cluster_address="gcomm://10.16.230.150,10.16.230.171,10.16.230.173"
wsrep_sst_method=xtrabackup-v2
wsrep-new-cluster
wsrep_node_name = lab1
wsrep_node_address="10.16.230.150"

wsrep_sst_donor=lab1
wsrep_sst_auth='backup:backup'

Im not sure, why its not taking the user; backup for the innobackupex user.

Please guide on fixing this.

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