galera.md

Galera Cluster

You can use this role to cluster multiple MariaDB servers using Galera. Please consider reading Galera's documentation first, to get a basic understanding of how Galera works.

Three-node cluster example

This is the simplest version of a cluster. It has to have at least three nodes for quorum reasons.

Say we have three nodes in our inventory: db01, db02 and db03. Additionally we put them into a group called db. Now we have to configure the database setting like above but with additional cluster variables.

So we put the definitions for the database we want to create on the cluster into the group_vars of db:

group_vars/db.yaml:

mariadb:
  users:
    cms:
      privileges:
        cms_all:
        cms_readall: "mydb.*:select,show view"
  my.cnf:
    mysqld:
       binlog_format: ROW
    galera:
      wsrep_on: "ON"
      wsrep_provider: /usr/lib/libgalera_smm.so
      wsrep_cluster_name: '"galera-dev-cluster1"'
      wsrep_cluster_address: "\"gcomm://172.17.78.1,172.17.78.2,172.27.78.3\""
  galera:
    cluster_nodes: 172.17.78.1,172.17.78.2,172.27.78.3

Note the settings for my.cnf.

Now we configure the settings for the individual hosts:

host_vars/db1.yaml:

---
mariadb:
  cms:
    hosts: 172.17.78.1
  galera:
    cluster: yes
    initializer: yes

This node is the initializer, which means the cluster is bootstrapped on this node and the other nodes join into the bootstrapped cluster.

host_vars/db2.yaml:

---
mariadb:
  users:
    cms:
      hosts:
        cms: 172.17.78.2
  galera:
    cluster: yes

host_vars/db3.yaml:

---
mariadb:
  users:
    cms:
      hosts:
        cms: 172.17.78.3
  galera:
    cluster: yes

Now you can run your playbook and the cluster will be set up

Two-node cluster example with additional arbitrator node using garbd

This is a special case of a two-node cluster that will not result in a split-brain scenario, because of the arbitrator node. The arbitrator node does not store the actual data, but will record the positions and vote in the quorum.

Please be sure you read Galera's documentation for this case and understand the consequences, before using this.

host_vars/db1.yaml:

---
mariadb:
  cms:
    hosts: 172.17.78.1
  galera:
    cluster: yes
    initializer: yes

This node is the initializer, which means the cluster is bootstrapped on this node and the other nodes join into the bootstrapped cluster.

host_vars/db2.yaml:

---
mariadb:
  users:
    cms:
      hosts:
        cms: 172.17.78.2
  galera:
    cluster: yes

host_vars/db3.yaml:

---
mariadb:
  users:
    cms:
      hosts:
        cms: 172.17.78.3
  galera:
    cluster: yes
    arbitrator: yes

Now you can run your playbook and the cluster will be set up