Galera

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Galera is a synchronous multi-master cluster for MySQL/InnoDB databases.

Note: Currently replication is supported only for InnoDB tables.

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: 

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.: 

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: 

wsrep_cluster_name='my_galera_cluster'

Also, set wsrep_sst_method to the desired state snapshot transfer method, the preferred one is rsync. 

wsrep_sst_method=rsync

Make sure you also set the following options: 

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: 

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

See also