[Pacemaker] 2 node failover cluster + MySQL Master-Master replica setup

[Dan Frincu]

Hi,

Ruzsinszky Attila wrote:
>> You're not making sense, first you say MySQL Master-Master, then you
>> mention master mysqld on clusterB and slave mysqld on clusterA. So,
>> which one is it:
>>     
> Yes, it is true. If I stop openais and I start mysql without openais the config
> is M-M (or Multi-Master).
>
> When pacemaker starts mysql processes I can see master and slave mysqld
> text from crm_mon.
>
>   
>> - MySQL Master-Master (or Multi-Master) which can be achieved via MySQL
>> Replication
>> - MySQL Master-Slave, which can be achieved via MySQL Replication as well
>>     
> I'd like to implement the above. I don't know which one is right for me.
> Because of M-M MySQL config I think the 1st one is my choice.
>   
A MySQL Multi-Master architecture for a 2 node setup brings a lot of 
configuration and administration overhead and has no conflict detection 
or resolution. Integrating such a setup with Pacemaker only adds to the 
overhead, as the current resource agents only handle a standalone MySQL 
server. Even the LSB script doesn't handle a Multi-Master setup. You'd 
have to write a custom resource agent, and it would probably fit your 
setup and your setup alone, meaning it couldn't be widely used for other 
setups, I know I had to make some modifications to the mysql resource 
agent and those changes were specific to my setup.

MySQL Cluster is a choice, it could be integrated with Pacemaker, 
although I don't actually see the benefits in this case, meaning MySQL 
Cluster would be the database backend, on it's own, doing it job, and to 
that backend you could connect from multiple frontends, put a load 
balancer (or two) before the frontends and you've got quite the setup, 
and the frontends and load balancer could be controlled by Pacemaker. 
But MySQL Cluster has it's downsides as well, it needs a minimum of 4 
nodes (it could probably work with less but that's the general 
recommendation), 2 data node, one SQL node and one management node. The 
SQL and management role could be collocated on one physical node + 2 
data nodes = 3 nodes.

Anyways, this is just to get a feel for what's involved in the process, 
and how Pacemaker would fit the picture, at least from my point of view.

I would recommend all questions related to MySQL Cluster, Replication, 
Multi-Master be directed to the appropriate mailing lists though, and if 
you want to write a resource agent for a Multi-Master setup, by all 
means, do share :)

Hope this helps.

Regards,
Dan
>   
>> - MySQL Master with a DRBD backend (even MySQL docs recommend this type
>> of setup for some use cases) in which the MySQL instance runs only where
>> DRBD is primary
>>     
> I think I know this setup and don't want it now.
>
>   
>> - MySQL Cluster (nothing to do with Pacemaker, although they can be put
>> together in a setup)
>>     
> This would be the next test if I have enough time.
>
> TIA,
> Ruzsi
>
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>   

-- 
Dan FRINCU
Systems Engineer
CCNA, RHCE
Streamwide Romania

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