Combining Different Member Versions in a Group account the major version. For example, if you have a group with members all running MySQL version 8.0.13: Note that joining members running releases before MySQL 5.7.27 check against all group members to find whether their own MySQL Server major version is lower. They therefore fail this check for a group where any members are running MySQL 8.0 releases, and cannot join the group even if it already has other members running MySQL 5.7. From MySQL 5.7.27, joining members only check against the group members that are running the lowest major version, so they can join a mixed version group where other MySQL 5.7 servers are present. In a multi-primary mode group with members that use different MySQL Server versions, Group Replication automatically manages the read-write and read-only status of members running MySQL 8.0.17 or higher. If a member leaves the group, the members running the version that is now the lowest are automatically set to read-write mode. When you change a group that was running in single-primary mode to run in multi- primary mode, using the  group_replication_switch_to_multi_primary_mode()  function, Group Replication automatically sets members to the correct mode. Members are automatically placed in read- only mode if they are running a higher MySQL server version than the lowest version present in the group, and members running the lowest version are placed in read-write mode. During an online upgrade procedure, if the group is in single-primary mode, all the servers that are not currently offline for upgrading function as they did before. The group elects a new primary whenever necessary, following the election policies described in Section 18.1.3.1, “Single-Primary Mode” . Note that if you require the primary to remain the same throughout (except when it is being upgraded itself), you must first upgrade all of the secondaries to a version higher than or equal to the target primary member version, then upgrade the primary last. The primary cannot remain as the primary unless it is running the lowest MySQL Server version in the group. After the primary has been upgraded, you can use the group_replication_set_as_primary()  function to reappoint it as the primary. If the group is in multi-primary mode, fewer online members are available to perform writes during the upgrade procedure, because upgraded members join in read-only mode after their upgrade. From MySQL 8.0.17, this applies to upgrades between patch versions, and for lower releases, this only applies to upgrades between major versions. When all members have been upgraded to the same release, from MySQL 8.0.17, they all change back to read-write mode automatically. For earlier releases, you must set super_read_only  to  OFF  manually on each member that should function as a primary following the upgrade. To deal with a problem situation, for example if you have to roll back an upgrade or add extra capacity to a group in an emergency, it is possible to allow a member to join an online group although it is running a lower MySQL Server version than the lowest version in use by other group members. The Group Replication system variable  group_replication_allow_local_lower_version_join  can be used in such situations to override the normal compatibility policies. It is important to note that setting the option to  ON  does not make the new member compatible with the group, and allows it to join the group without any safeguards against incompatible behaviors by the existing members. The option must therefore only be used carefully in specific situations, and you must take additional precautions to avoid the new member failing due to normal group activity. For details of these precautions, see the description for group_replication_allow_local_lower_version_join . 3788 18.8.1.1 Member Versions During Upgrades •A member that is running MySQL version 5.7 does not join. •A member running MySQL 8.0.16 joins normally (because it considers the major version). •A member running MySQL 8.0.17 joins but remains in read-only mode (because it considers the patch version).