START GROUP_REPLICATION
          [USER='user_name']
          [, PASSWORD='user_pass']
          [, DEFAULT_AUTH='plugin_name']

Starts group replication. This statement requires the GROUP_REPLICATION_ADMIN privilege (or the deprecated SUPER privilege). If super_read_only=ON is set and the member should join as a primary, super_read_only is set to OFF once Group Replication successfully starts.

A server that participates in a group in single-primary mode should use skip_replica_start=ON. Otherwise, the server is not allowed to join a group as a secondary.

You can specify user credentials for distributed recovery in the START GROUP_REPLICATION statement using the USER, PASSWORD, and DEFAULT_AUTH options, as follows:

These credentials are used for distributed recovery on the group_replication_recovery channel. When you specify user credentials on START GROUP_REPLICATION, the credentials are saved in memory only, and are removed by a STOP GROUP_REPLICATION statement or server shutdown. You must issue a START GROUP_REPLICATION statement to provide the credentials again. This method is therefore not compatible with starting Group Replication automatically on server start, as specified by the group_replication_start_on_boot system variable.

User credentials specified on START GROUP_REPLICATION take precedence over any user credentials set for the group_replication_recovery channel using a CHANGE REPLICATION SOURCE TO. Note that user credentials set using these statements are stored in the replication metadata repositories, and are used when START GROUP_REPLICATION is specified without user credentials, including automatic starts if the group_replication_start_on_boot system variable is set to ON. To gain the security benefits of specifying user credentials on START GROUP_REPLICATION, ensure that group_replication_start_on_boot is set to OFF (the default is ON), and clear any user credentials previously set for the group_replication_recovery channel, following the instructions in Section 20.6.3, “Securing Distributed Recovery Connections”.

While a member is rejoining a replication group, its status can be displayed as OFFLINE or ERROR before the group completes the compatibility checks and accepts it as a member. When the member is catching up with the group's transactions, its status is RECOVERING.