Galera is a synchronous multi-master cluster for MySQL/InnoDB databases.
Installation
The two components Galera cluster comprised of are Galera plugin itself and a patched version of MySQL server which connect using wsrep API.
Install the galera package. Also you will need rsync and lsof packages for rsync method.
Start/Enable the mysqld.service daemon.
Configuration
You need to configure the cluster.
On each node edit /etc/my.cnf.d/server.cnf and update the wsrep_cluster_address variable so it contains the list of all nodes in the cluster:
/etc/my.cnf.d/server.cnf
wsrep_cluster_address="gcomm://192.168.1.4,192.168.1.5,192.168.1.6"
Change the variables wsrep_node_address and wsrep_node_name to the IP address/hostname and name (this does not need to be unique) for each node, e.g.:
/etc/my.cnf.d/server.cnf
wsrep_node_address='192.168.1.4' wsrep_node_name='node1'
The wsrep_cluster_name variable should contain the same name for all cluster nodes:
/etc/my.cnf.d/server.cnf
wsrep_cluster_name='my_galera_cluster'
Also, set wsrep_sst_method to the desired state snapshot transfer method, the preferred one is rsync.
/etc/my.cnf.d/server.cnf
wsrep_sst_method=rsync
Make sure you also set the following options:
/etc/my.cnf.d/server.cnf
wsrep_on=ON wsrep_provider=/usr/lib/galera/libgalera_smm.so default_storage_engine=InnoDB innodb_autoinc_lock_mode=2 binlog_format=row
When you have finished with /etc/my.cnf.d/server.cnf, bootstrap the mysqld service on the first node (ONLY on the first node):
# galera_new_cluster
This will bootstrap the cluster. Use MySQL's command line tool to log in as root into your MySQL server:
$ mysql -p -u root
Check the status of the cluster, this will show you wsrep-related status variables:
mysql> SHOW STATUS LIKE 'wsrep_%';
| wsrep_local_state | 4 | | wsrep_local_state_comment | Synced | | wsrep_cert_index_size | 0 | | wsrep_causal_reads | 0 | | wsrep_incoming_addresses | 192.168.1.4:3306 | | wsrep_cluster_conf_id | 1 | | wsrep_cluster_size | 1 | | wsrep_cluster_state_uuid | 6cd96745-2ea8-11e3-bbc8-d666651b51ef | | wsrep_cluster_status | Primary | | wsrep_connected | ON | | wsrep_local_index | 0 | | wsrep_provider_name | Galera |
If you use the xtrabackup or mysqldump SST method, you will need to create a MySQL user for sst transfers.
Once you configured the first node, you should be able to start mysqld.service.