Mysql – Group replication ports issues

The MySQL error log should have some clues. Can you show the log snippet from just after you issue START GROUP_REPLICATION?

Edit: after seeing the MySQL error log snippet...

It looks like you're perhaps using the same port for the mysql protocol and the GCS (group communication system)?

You have to use different ports. For example, in your config:

[mysqld]
port=3307
group_replication_local_address = '10.32.6.48:6606'
group_replication_group_seeds = '10.32.6.49:6606,10.32.6.50:6606'

So, I actually had several issues that may come in handy to walk through for others:

Error: 2003

I removed the bind-address from the master

Errno: 1045

Access denied for user

I explicitly set the IP address for the slave user:

GRANT REPLICATION SLAVE ON *.* TO 'slave_user'@'000.000.000.00' IDENTIFIED BY 'password';

instead of

GRANT REPLICATION SLAVE ON *.* TO 'slave_user'@'%' IDENTIFIED BY 'password';

Error 1236

Got fatal error 1236 from master when reading data from binary log: 'log event entry exceeded max_allowed_packet

It turns out the default max_allowed_packet is 1MB for <= 5.6.5 and 4MB for >= 5.6.6.

I set both of these manually to 16MB as per this article

Error 1236

Got fatal error 1236 from master when reading data from binary log: 'bogus data in log event

I followed the instructions in this answer

That solved the last of my errors and the replication appears to be working as expected now!