Galera Replication

Galera replication is a third party open source replication utility for MySQL.Follow the below steps for setting up galera replication on all the three nodes intended for galera replication.:
1.On each node create a galera repo file as /etc/yum.repos.d/galera and put the below entries
[galera]
name = Galera
baseurl = http://releases.galeracluster.com/galera-3/centos/7/x86_64/
gpgkey = http://releases.galeracluster.com/GPG-KEY-galeracluster.com
gpgcheck = 1

[mysql-wsrep]
name = MySQL-wsrep
baseurl = http://releases.galeracluster.com/mysql-wsrep-5.7.21-25.14/centos/7/x86_64/
gpgkey = http://releases.galeracluster.com/GPG-KEY-galeracluster.com
gpgcheck = 1

2.Install galera and mysql-wsrep using the below yum install commands
yum install galera-3 
yum install mysql-wsrep-5.7

3.Edit the /etc/my.cnf file and put the below entries in the file
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
user=mysql
binlog_format=ROW
bind-address=0.0.0.0
default_storage_engine=innodb
innodb_autoinc_lock_mode=2
innodb_flush_log_at_trx_commit=0
innodb_buffer_pool_size=122M
wsrep_provider=/usr/lib64/galera-3/libgalera_smm.so
wsrep_provider_options="gcache.size=300M; gcache.page_size=300M"
wsrep_cluster_name="gmmcluster"
#wsrep_cluster_address="gcomm://192.168.1.33:3306,192.168.1.34:3306,192.168.1.19:3306"
wsrep_cluster_address="gcomm://192.168.1.33,192.168.1.34,192.168.1.19"
wsrep_sst_method=rsync

server_id=1
srep_node_address="192.168.1.33"
wsrep_node_name="gmm-1"

[mysql_safe]
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid

4.In the first node run the below command to start mysql deamon in bootstrap mode
/usr/bin/mysqld_bootstrap

5.Login to mysql prompt and run the below queries to validate if galera replication is enabled
show status like 'wsrep_cluster_size';
show status like '%version%';
show variables like 'innodb_file_format';

6.On second and third run , start the mysql deamon using systemctl
systemctl start mysqld

7.Now if we check we can see 3 as cluster size for wsrep_cluster_size query
show status like 'wsrep_cluster_size';

8.Create data in any of the nodes and validate if it is getting replicated in other nodes.This confirms the galera multi master replication being setup in your system.

If by any chance , any one of the nodes goes down in galera replication.check the below file
cat /var/lib/mysql/grastate.dat

Whichever node doesn't come up will have safe_to_bootstrap as 1 in the grastate.dat file.
On that node start bootstrap replication
/usr/bin/mysqld_bootstrap