openstack/openstack-ansible
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openstack-ansible/doc/source/install-guide/ops-galera-recoverysingle.rst
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Home OpenStack Ansible Installation Guide

Single-node failure

If a single node fails, the other nodes maintain quorum and continue to process SQL requests.

  1. Run the following Ansible command to determine the failed node:

    $ ansible galera_container -m shell -a "mysql -h localhost\
 -e 'show status like \"%wsrep_cluster_%\";'"
node3_galera_container-3ea2cbd3 | FAILED | rc=1 >>
ERROR 2002 (HY000): Can't connect to local MySQL server through
socket '/var/run/mysqld/mysqld.sock' (111)

node2_galera_container-49a47d25 | success | rc=0 >>
Variable_name             Value
wsrep_cluster_conf_id     17
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     17
wsrep_cluster_size        3
wsrep_cluster_state_uuid  338b06b0-2948-11e4-9d06-bef42f6c52f1
wsrep_cluster_status      Primary

    In this example, node 3 has failed.

  2. Restart MariaDB on the failed node and verify that it rejoins the cluster.

  3. If MariaDB fails to start, run the mysqld command and perform further analysis on the output. As a last resort, rebuild the container for the node.