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Home OpenStack Ansible Installation Guide

Starting a cluster

Gracefully shutting down all nodes destroys the cluster. Starting or restarting a cluster from zero nodes requires creating a new cluster on one of the nodes.

  1. The new cluster should be started on the most advanced node. Run the following command to check the seqno value in the grastate.dat file on all of the nodes:

    $ ansible galera_container -m shell -a "cat /var/lib/mysql/grastate.dat"
node2_galera_container-49a47d25 | success | rc=0 >>
# GALERA saved state version: 2.1
uuid:    338b06b0-2948-11e4-9d06-bef42f6c52f1
seqno:   31
cert_index:

node3_galera_container-3ea2cbd3 | success | rc=0 >>
# GALERA saved state version: 2.1
uuid:    338b06b0-2948-11e4-9d06-bef42f6c52f1
seqno:   31
cert_index:

node4_galera_container-76275635 | success | rc=0 >>
# GALERA saved state version: 2.1
uuid:    338b06b0-2948-11e4-9d06-bef42f6c52f1
seqno:   31
cert_index:

    In this example, all nodes in the cluster contain the same positive seqno values because they were synchronized just prior to graceful shutdown. If all seqno values are equal, any node can start the new cluster.

    $ /etc/init.d/mysql start --wsrep-new-cluster

    This command results in a cluster containing a single node. The wsrep_cluster_size value shows the number of nodes in the cluster.

    node2_galera_container-49a47d25 | FAILED | rc=1 >>
ERROR 2002 (HY000): Can't connect to local MySQL server
through socket '/var/run/mysqld/mysqld.sock' (111)

node3_galera_container-3ea2cbd3 | FAILED | rc=1 >>
ERROR 2002 (HY000): Can't connect to local MySQL server
through socket '/var/run/mysqld/mysqld.sock' (2)

node4_galera_container-76275635 | success | rc=0 >>
Variable_name             Value
wsrep_cluster_conf_id     1
wsrep_cluster_size        1
wsrep_cluster_state_uuid  338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status      Primary

  2. Restart MariaDB on the other nodes and verify that they rejoin the cluster.

    node2_galera_container-49a47d25 | success | rc=0 >>
Variable_name             Value
wsrep_cluster_conf_id     3
wsrep_cluster_size        3
wsrep_cluster_state_uuid  338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status      Primary

node3_galera_container-3ea2cbd3 | success | rc=0 >>
Variable_name             Value
wsrep_cluster_conf_id     3
wsrep_cluster_size        3
wsrep_cluster_state_uuid  338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status      Primary

node4_galera_container-76275635 | success | rc=0 >>
Variable_name             Value
wsrep_cluster_conf_id     3
wsrep_cluster_size        3
wsrep_cluster_state_uuid  338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status      Primary