How to change MySQL InnoDB cluster from single primary mode to multi primary mode? My goal is to setup, in a lab environment, a MySQL InnoDB cluster in multi-primary mode.

I have read much, but I cannot get this setup to work.

Ubuntu 16.04.3 server LTS x 3
SQL0 - SQL2

Ubuntu 16.04.3 server LTS x 2
REP0 - REP1

All server instances are in Virtual machine except REP0 is on bare metal and REP1 is off line.

Installed MySQL server 8.0 from Oracle APT repo using mysql-apt-config_0.8.10-1_all.deb.

These servers have been up and down with many config changes trying to find a setup that works.

Set MySQL server 8.0 with Legacy Authentication Method on all boxes.

My current /etc/mysql/my.cnf is based on Justin Ellingwood @ DigitalOcean.

This is /etc/mysql/my.cnf from SQL0. This machine was at one time the primary in a single-primary setup that did not work correctly. 

The other /etc/mysql/my.cnf file are very similar to this one with the # Host specific replication configuration section changed.

The error I am trying to resolve now is from /var/log/mysql/error.log.

[ERROR] Plugin group_replication reported: 'It is not allowed to run single primary mode with 'enforce_update_everywhere_checks' enabled.'


Yes I do have these set in my.cnf because I want multi-primary mode. I do not want to run in single-primary mode.

loose-group_replication_single_primary_mode = OFF
loose-group_replication_enforce_update_everywhere_checks = ON


Where, How, What else do I need to change for these to be in multi-primary mode and not error out?
Any reason why you're not using MySQL Shell and its AdminAPI to set up and manage your InnoDB cluster?

You can create a multi-primary cluster very easily using the AdminAPI. Example:

var cluster = dba.createCluster("myCluster", {multiPrimary: true})


Also, if you already have a running Group Replication group that you'd like to manage using the Shell you can simply "adopt" it:

var cluster = dba.createCluster("myCluster", {adoptFromGR: true})


And since 8.0.14, you can change a running InnoDB cluster from single-primary mode to multi-primary mode "live". The AdminAPI provides a function for that operation:

&lt;Cluster.&gt;switchToMultiPrimaryMode()&gt;


Also, it is possible to switch back a running cluster to single-primary mode:

&lt;Cluster.&gt;switchToSinglePrimaryMode([instance])


And even to elect a member of the cluster to be the new primary:

&lt;Cluster.&gt;setPrimaryInstance(instance)


Please take a look at the blog post that announced those new features:

https://mysqlserverteam.com/mysql-innodb-cluster-changing-cluster-topology-modes-live/

And for further information check the official userguide.

Cheers,

Miguel