Re: How to upgrade multi-master from 5.6 > 5.7

[Rick James]

Since the Slave is "unused", I will make use of it. (If it is in use, first clone it as another Slave of B. Let's call this Slave Machine C.

Using the notation that '*A6' means Machine A running 5.6 and accepting Writes. The arrows indicate which way data is replicating.

*A6 <-> *B6 -> C6 -- current setup
*A6 <-> *B6 - C6 -- disconnect
*A6 <-> *B6 - C7 -- install 5.7 and run mysql_upgrade. No replication yet.
*A6 <-> *B6 - C7 - D7 -- Clone C7 onto new machine D
(About now, you could Clone C or D to get a new Slave E7; details omitted.)
*A6 <-> *B6 - C7 -> D7 -- turn on repl (won't be any activity yet)
*A6 <-> *B6 -> C7 -> D7 -- turn on repl
Test reads to C and D -- there could be upgrade issues, such as new keywords.
A6 <-> *B6 -> C7 -> D7 -- starting to get rid of A; all writes go to B
A6 -> B6 -> *C7 -> D7 -- switch from B to C as the sole master
A6 -> B6 -> *C7 -> D7 -- Wait for all writes to A and B to be copied to C
*C7 -> D7 -- remove A and B; wait for D to catch up
*C7 <-> *D7 -- back to Dual-Master

Be sure to have log_bin and log_slave_updates on. And distinct server_id values.

Caveat: I have not performed this exercise. In proofreading the steps, verify whether all the data is up to date on all machines -- or understand that replication is still connected in order to allow for "catching up".