How does Group Replication use network addresses and hostnames? How does Group Replication use network addresses and hostnames? Group Replication uses network connections between members and therefore its functionality is directly impacted by how you configure hostnames and ports. For example, Group Replication’s distributed recovery process creates a connection to an existing group member using the server’s hostname and port. When a member joins a group it receives the group membership information, using the network address information that is listed at  performance_schema.replication_group_members . One of the members listed in that table is selected as the donor of the missing data from the group to the joining member. This means that any value you configure using a hostname, such as the SQL network address or the group seeds address, must be a fully qualified name and resolvable by each member of the group. You can ensure this for example through DNS, or correctly configured  /etc/hosts  files, or other local processes. If a you want to configure the  MEMBER_HOST  value on a server, specify it using the  --report-host option on the server before joining it to the group. The assigned value is used directly and is not affected by the skip_name_resolve  system variable. Important To configure  MEMBER_PORT  on a server, specify it using the  report_port  system variable. Why did the auto increment setting on the server change? When Group Replication is started on a server, the value of  auto_increment_increment  is changed to the value of  group_replication_auto_increment_increment , which defaults to 7, and the value of  auto_increment_offset  is changed to the server ID. The changes are reverted when Group Replication is stopped. These settings avoid the selection of duplicate auto-increment values for writes on group members, which causes rollback of transactions. The default auto increment value of 7 for Group Replication represents a balance between the number of usable values and the permitted maximum size of a replication group (9 members). The changes are only made and reverted if  auto_increment_increment  and auto_increment_offset  each have their default value of 1. If their values have already been modified from the default, Group Replication does not alter them. From MySQL 8.0, the system variables are also not modified when Group Replication is in single-primary mode, where only one server writes. How do I find the primary? If the group is operating in single-primary mode, it can be useful to find out which member is the primary. See Finding the Primary 3838