Adding Nodes to Cluster

New nodes <Node> that are properly configured are provisioned automatically. When you start a node with the address of at least one other running node in the wsrep_cluster_address variable, it automatically joins the cluster and synchronizes with it.

Note

Any existing data and configuration will be overwritten to match the data and configuration of the DONOR node. Do not join several nodes at the same time to avoid overhead due to large amounts of traffic when a new node joins.

By default, Percona XtraDB Cluster uses Percona XtraBackup for State Snapshot Transfer (SST). This requires the following:

• Set the wsrep_sst_method variable to xtrabackup-v2 and provide SST user credentials with the wsrep_sst_auth variable.

For more information, see Configuring Nodes for Write-Set Replication.

• Create a user for SST on the initial node.

For more information, see Bootstrapping the First Node.

Starting the Second Node

Start the second node by using either of the following commands:

[root@pxc2 ~]# /etc/init.d/mysql start

or

[root@pxc2 ~]# systemctl start mysql

After the server starts, it should receive SST automatically.

To check the status of the second node, run the following:

mysql@pxc2> show status like 'wsrep%';

The output shows that the new node has been successfully added to the cluster. Cluster size is now 2 nodes, it is the primary component, and it is fully connected and ready to receive write-set replication.

+----------------------------+--------------------------------------+
| Variable_name              | Value                                |
+----------------------------+--------------------------------------+
| wsrep_local_state_uuid     | c2883338-834d-11e2-0800-03c9c68e41ec |
| ...                        | ...                                  |
| wsrep_local_state          | 4                                    |
| wsrep_local_state_comment  | Synced                               |
| ...                        | ...                                  |
| wsrep_cluster_size         | 2                                    |
| wsrep_cluster_status       | Primary                              |
| wsrep_connected            | ON                                   |
| ...                        | ...                                  |
| wsrep_ready                | ON                                   |
+----------------------------+--------------------------------------+
40 rows in set (0.01 sec)

If the state of the second node is Synced as in the previous example, then the node received full SST, is synchronized with the cluster, and you can proceed to add the next node.

Note

If the state of the node is Joiner, it means that SST hasn’t finished. Do not add new nodes until all others are in Synced state.

Starting the Third Node

To add the third node, start the node using either command:

[root@pxc3 ~]# /etc/init.d/mysql start

or

[root@pxc3 ~]# systemctl start mysql

To check the status of the third node, run the following:

mysql@pxc3> show status like 'wsrep%';

The output shows that the new node has been successfully added to the cluster. Cluster size is now 3 nodes, it is the primary component, and it is fully connected and ready to receive write-set replication.

+----------------------------+--------------------------------------+
| Variable_name              | Value                                |
+----------------------------+--------------------------------------+
| wsrep_local_state_uuid     | c2883338-834d-11e2-0800-03c9c68e41ec |
| ...                        | ...                                  |
| wsrep_local_state          | 4                                    |
| wsrep_local_state_comment  | Synced                               |
| ...                        | ...                                  |
| wsrep_cluster_size         | 3                                    |
| wsrep_cluster_status       | Primary                              |
| wsrep_connected            | ON                                   |
| ...                        | ...                                  |
| wsrep_ready                | ON                                   |
+----------------------------+--------------------------------------+
40 rows in set (0.01 sec)

Next Steps

When you add all nodes to the cluster, you can verify replication by running queries and manipulating data on nodes to see if these changes are synchronized accross the cluster.