Galera is a synchronous multi-master cluster for MySQL/InnoDB databases.
The two components Galera cluster comprised of are Galera plugin itself and a patched version of MySQL server which connect using wsrep API.
You need to configure the cluster.
On each node edit
/etc/mysql/my.cnf and update the wsrep_cluster_address variable so it contains the list of all nodes in the cluster:
Change the variables wsrep_node_address and wsrep_node_name to the IP address/hostname and name(this doesn't need to be unique) for each node, e.g.:
The wsrep_cluster_name variable should contain the same name for all cluster nodes:
Also, set wsrep_sst_method to the desired state snapshot transfer method, the preferred one is rsync.
When you have finished with
/etc/mysql/my.cnf, start the mysqld service on the first node:
# systemctl start mysqld-bootstrap.service
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:
mysql> SHOW STATUS LIKE 'wsrep_%';
This will show you wsrep-related status variables:
... | 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 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 all other nodes with:
# systemctl start mysqld.service