22.214.171.124 User Credentials
Group Replication uses the asynchronous replication protocol to achieve Section 17.9.5, “Distributed Recovery”, synchronizing group members before joining them to the group. The distributed recovery process relies on a replication channel named
group_replication_recovery which is used to transfer transactions from donor members to members that join the group. Therefore you need to set up a replication user with the correct permissions so that Group Replication can establish direct member-to-member recovery replication channels.
Start the MySQL server instance and then connect a client to it. Create a MySQL user with the
REPLICATION SLAVE privilege. This process can be captured in the binary log and then you can rely on distributed recovery to replicate the statements used to create the user. Alternatively, you can disable binary logging using
SET SQL_LOG_BIN=0; and then create the user manually on each member, for example if you want to avoid the changes being propagated to other server instances. If you do decide to disable binary logging, ensure you renable it once you have configured the user.
In the following example the user
rpl_user with the password
password is shown. When configuring your servers use a suitable user name and password.
mysql> CREATE USER rpl_user@'%' IDENTIFIED BY 'password'; mysql> GRANT REPLICATION SLAVE ON *.* TO rpl_user@'%'; mysql> FLUSH PRIVILEGES;
If binary logging was disabled, enable it again once the user has been created using
Once the user has been configured, use the
CHANGE MASTER TO statement to configure the server to use the given credentials for the
group_replication_recovery replication channel the next time it needs to recover its state from another member. Issue the following, replacing
password with the values used when creating the user.
mysql> CHANGE MASTER TO MASTER_USER='rpl_user', MASTER_PASSWORD='password' \\ FOR CHANNEL 'group_replication_recovery';
Distributed recovery is the first step taken by a server that joins the group and does not have the same set of transactions as the group members. If these credentials are not set correctly for the
group_replication_recovery replication channel and the
rpl_user as shown, the server cannot connect to the donor members and run the distributed recovery process to gain synchrony with the other group members, and hence ultimately cannot join the group. See Section 17.9.5, “Distributed Recovery”.
Similarly, if the server cannot correctly identify the other members via the server's
hostname the recovery process can fail. It is recommended that operating systems running MySQL have a properly configured unique
hostname, either using DNS or local settings. This
hostname can be verified in the
Member_host column of the
performance_schema.replication_group_members table. If multiple group members externalize a default
hostname set by the operating system, there is a chance of the member not resolving to the correct member address and not being able to join the group. In such a situation use
report_host to configure a unique
hostname to be externalized by each of the servers.