When a member joins the group, distributed recovery is carried out using a combination of a remote cloning operation, if available and appropriate, and an asynchronous replication connection. For a full description of distributed recovery, see Section 18.5.3, “Distributed Recovery”.
The connection that an existing member offers to a joining member
for distributed recovery is not the same connection that is used
by Group Replication for communication between online members of
the group. Up to MySQL 8.0.20, group members offer their standard
SQL client connection to joining members for distributed recovery,
as specified by MySQL Server's
port system variables. From MySQL
8.0.21, group members may advertise an alternative list of
distributed recovery endpoints as dedicated client connections for
joining members. For more details, see
Section 188.8.131.52, “Connections for Distributed Recovery”.
To secure distributed recovery connections in the group, ensure that user credentials for the replication user are properly secured, and use SSL for distributed recovery connections if possible.