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Expanding Galera cluster


Hi guys,

I need some help as I'm preparing to expand my existing Galera cluster.
Generally the purpose of it is I need to replace 3 VMs I have a cluster
running on to 2 physical servers I have been given for that purpose.

My idea was to join 2 physical cluster to the existing cluster of 3 and
then remove all 3 VMs from the cluster leaving 2 physical nodes within. I
have a arbitrator box within the cluster as well.

The config at the moment contains 2 maxscale proxy nodes on the front
balancing the read queries across the entire cluster of 3 and write queries
to the elected master.

What I want to achieve is as I said above but + I will need another help
with maxscale to expand and then shrink the cluster down to 2 nodes
afterwards. I have had a situation before when I had to do a simple config
change on the Galera cluster and I was trying to mark nodes and put them
into maintenance mode to stop traffic coming to them but the commands like
set server NODE master didn't actually do anything. I had situations when I
had 2 masters in the cluster for a second because then something was
happening that my manually selected master was becoming a slave again. I
couldn't find anything on the internet what would point me into right
direction and explain the whole procedure in details.

My cluster is quite busy at the moment even overnight so there is no
perfect time to do anything on it. I need to do it the least disruptive way
and the most controlled way as well. Hence I'm asking for help and
suggestions as I found both Galera and maxscale documentation very very
brief not actually providing any decent details or procedures. I found much
more help from Percona but descriptions don't match sometimes.

Please help.


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