State transfer from the binary log requires a replication user with the correct permissions so that Group Replication can establish direct member-to-member replication channels. The same replication user is used for distributed recovery on all the group members. If group members have been set up to support the use of a remote cloning operation as part of distributed recovery, which is available from MySQL 8.0.17, this replication user is also used as the clone user on the donor, and requires the correct permissions for this role too. For detailed instructions to set up this user, see Section 22.214.171.124, “User Credentials For Distributed Recovery”.
To secure the user credentials, you can require SSL for connections with the user account, and (from MySQL 8.0.21) you can provide the user credentials when Group Replication is started, rather than storing them in the replica status tables. Also, if you are using caching SHA-2 authentication, you must set up RSA key-pairs on the group members.
By default, users created in MySQL 8 use Section 126.96.36.199, “Caching SHA-2 Pluggable Authentication”. If the replication user you configure for distributed recovery uses the caching SHA-2 authentication plugin, and you are not using SSL for distributed recovery connections, RSA key-pairs are used for password exchange. For more information on RSA key-pairs, see Section 6.3.3, “Creating SSL and RSA Certificates and Keys”.
In this situation, you can either copy the public key of the
rpl_user to the joining member, or
configure the donors to provide the public key when requested.
The more secure approach is to copy the public key of the
replication user account to the joining member. Then you need
to configure the
system variable on the joining member with the path to the
public key for the replication user account.
The less secure approach is to set
on donors so that they provide the public key of the
replication user account to joining members. There is no way
to verify the identity of a server, therefore only set
when you are sure there is no risk of server identity being
compromised, for example by a man-in-the-middle attack.
A replication user that requires an SSL connection must be created before the server joining the group (the joining member) connects to the donor. Typically, this is set up at the time you are provisioning a server to join the group. To create a replication user for distributed recovery that requires an SSL connection, issue these statements on all servers that are going to participate in the group:
mysql> SET SQL_LOG_BIN=0; mysql> CREATE USER 'rec_ssl_user'@'%' IDENTIFIED BY 'password' REQUIRE SSL; mysql> GRANT replication slave ON *.* TO 'rec_ssl_user'@'%'; mysql> GRANT BACKUP_ADMIN ON *.* TO 'rec_ssl_user'@'%'; mysql> FLUSH PRIVILEGES; mysql> SET SQL_LOG_BIN=1;
To supply the user credentials for the replication user, you
can set them permanently as the credentials for the
group_replication_recovery channel, using a
CHANGE MASTER TO statement.
Alternatively, from MySQL 8.0.21, you can specify them on the
statement each time Group Replication is started. User
credentials specified on
GROUP_REPLICATION take precedence over any user
credentials that have been set using a
CHANGE MASTER TO statement.
User credentials set using
TO are stored in plain text in the replication
metadata repositories on the server, but user credentials
GROUP_REPLICATION are saved in memory only, and are
removed by a
GROUP_REPLICATION statement or server shutdown.
to specify the user credentials therefore helps to secure the
Group Replication servers against unauthorized access.
However, this method is not compatible with starting Group
Replication automatically, as specified by the
If you want to set the user credentials permanently using a
CHANGE MASTER TO statement,
issue this statement on the member that is going to join the
mysql> CHANGE MASTER TO MASTER_USER='rec_ssl_user', MASTER_PASSWORD='password' FOR CHANNEL 'group_replication_recovery';
To supply the user credentials on
GROUP_REPLICATION, issue this statement when
starting Group Replication for the first time, or after a
mysql> START GROUP_REPLICATION USER='rec_ssl_user', PASSWORD='password';
If you switch to using
GROUP_REPLICATION to specify user credentials on a
server that previously supplied the credentials using
CHANGE MASTER TO, you must
complete the following steps to get the security benefits of
Stop Group Replication on the group member using a
STOP GROUP_REPLICATIONstatement. Although it is possible to take the following two steps while Group Replication is running, you need to restart Group Replication to implement the changes.
Set the value of the
group_replication_start_on_bootsystem variable to
OFF(the default is
Remove the distributed recovery credentials from the replica status tables by issuing this statement:
mysql> CHANGE MASTER TO MASTER_USER='', MASTER_PASSWORD='' FOR CHANNEL 'group_replication_recovery';
Restart Group Replication on the group member using a
START GROUP_REPLICATIONstatement that specifies the distributed recovery user credentials.
Without these steps, the credentials remain stored in the
replica status tables, and can also be transferred to other
group members during remote cloning operations for distributed
channel could then be inadvertently started with the stored
credentials, on either the original member or members that
were cloned from it. An automatic start of Group Replication
on server boot (including after a remote cloning operation)
would use the stored user credentials, and they would also be
used if an operator did not specify the distributed recovery
credentials on a