20.8.3.2 Upgrading a Group Replication Member

This section explains the steps required for upgrading a member of a group. This procedure is part of the methods described at Section 20.8.3.3, “Group Replication Online Upgrade Methods”. The process of upgrading a member of a group is common to all methods and is explained first. The way which you join upgraded members can depend on which method you are following, and other factors such as whether the group is operating in single-primary or multi-primary mode. How you upgrade the server instance, using either the in-place or provision approach, does not impact on the methods described here.

The process of upgrading a member consists of removing it from the group, following your chosen method of upgrading the member, and then rejoining the upgraded member to a group. The recommended order of upgrading members in a single-primary group is to upgrade all secondaries, and then upgrade the primary last. If the primary is upgraded before a secondary, a new primary using the older MySQL version is chosen, but there is no need for this step.

To upgrade a member of a group:

• Connect a client to the group member and issue STOP GROUP_REPLICATION. Before proceeding, ensure that the member's status is OFFLINE by monitoring the replication_group_members table.

• Disable Group Replication from starting up automatically so that you can safely connect to the member after upgrading and configure it without it rejoining the group by setting group_replication_start_on_boot=0.

  Important

  If an upgraded member has group_replication_start_on_boot=1 then it could rejoin the group before you can perform the MySQL upgrade procedure and could result in issues. For example, if the upgrade fails and the server restarts again, then a possibly broken server could try to join the group.

• Stop the member, for example using mysqladmin shutdown or the SHUTDOWN statement. Any other members in the group continue running.

• Upgrade the member, using the in-place or provisioning approach. See Chapter 3, Upgrading MySQL for details. When restarting the upgraded member, because group_replication_start_on_boot is set to 0, Group Replication does not start on the instance, and therefore it does not rejoin the group.

• Once the MySQL upgrade procedure has been performed on the member, group_replication_start_on_boot must be set to 1 to ensure Group Replication starts correctly after restart. Restart the member.

• Connect to the upgraded member and issue START GROUP_REPLICATION. This rejoins the member to the group. The Group Replication metadata is in place on the upgraded server, therefore there is usually no need to reconfigure Group Replication. The server has to catch up with any transactions processed by the group while the server was offline. Once it has caught up with the group, it becomes an online member of the group.

  Note

  The longer it takes to upgrade a server, the more time that member is offline and therefore the more time it takes for the server to catch up when added back to the group.

When an upgraded member joins a group which has any member running an earlier MySQL Server version, the upgraded member joins with super_read_only=on. This ensures that no writes are made to upgraded members until all members are running the newer version. In a multi-primary mode group, when the upgrade has been completed successfully and the group is ready to process transactions, members that are intended as writeable primaries must be set to read-write mode. As of MySQL 8.0.17, when all members of a group have been upgraded to the same release, they all change back to read-write mode automatically. For earlier releases you must set each member manually to read-write mode. Connect to each member and issue:

SET GLOBAL super_read_only=OFF;