MySQL 5.7 Release Notes
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 SET SQL_LOG_BIN=1;.
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
rpl_user and
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.