Galera Cluster – 3rd Quorum Only Node Without Replication

galerahigh-availabilitymariadbmariadb-10.1

I want to setup a 2 node cluster for MariaDB Galera cluster. What I read says it "requires" 3 nodes minimum. This is not correct, I am familiar with HA through using pacemaker, and basically, with only 2 nodes, you don't have quorum, which Galera Cluster Uses.

I found a good article, which basically explains, the 2 options I already figured existed.

Option 1:

Disable Quorum Check

SET GLOBAL wsrep_provider_options='pc.ignore_sb=TRUE';

Option 2:

Post Split-Brain, manually tell a node to become Primary

SET GLOBAL wsrep_provider_options='pc.bootstrap=YES';

What I'd like, is to set up a 3rd VM, that doesn't replicate any DB's, but acts an a quorum box.

Is this possible? Any links on HowTo? – Maybe I am over-thinking this, is there a way to join a cluster, but not define any Databases to replicate? (Seemed to me when I set up Galera that it just replicated everything automatically, which is good, but I'm not so sure there is a "don't replicate option")

http://galeracluster.com/documentation-webpages/twonode.html

Best Answer

The GALERA ARBITRATOR is exactly what I needed.

  • The recommended deployment of Galera Cluster is that you use a minimum of three instances. Three nodes, three datacenters and so on.

    • In the event that the expense of adding resources, such as a third datacenter, is too costly, you can use Galera Arbitrator. Galera Arbitrator is a member of the cluster that participates in voting, but not in the actual replication."

Galera Arbitrator serves two purposes:

  • When you have an even number of nodes, it functions as an odd node, to avoid split-brain situations.

  • It can request a consistent application state snapshot, for use in making backups.

HowTo:

http://galeracluster.com/documentation-webpages/arbitrator.html

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