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Pacemaker does not promote a node to master until it received from all nodes the latest Sequence number (seqno). That is a problem when one node of the MariaDB Galera Cluster is down (eg. due to hardware or network problems) because the Sequence number can not be received from the unavailable node. To recover a MariaDB Galera Cluster manual steps are needed to select a bootstrap node for MariaDB Galera Cluster and to promote that node with Pacemaker.
Selecting the correct bootstrap node (depending on the highest Sequence number (seqno)) is important. If the wrong node is selected data loss is possible.
To find out which node has the latest Sequence number, call the following command on all MariaDB Galera Cluster nodes and select the node with the highest Sequence number.
mysqld_safe --wsrep-recover
tail -5 /var/log/mysql/mysqld.log
...
[Note] WSREP: Recovered position: 7a477edc-757d-11e9-a01a-d218e7381711:2490
At the end of /var/log/mysql/mysqld.log the Sequence
number is written (in this example, the sequence number is 2490).
After all Sequence numbers are collected from all nodes, the node with
the highest Sequence number is selected for bootstrap node.
In this example, the node with the highest Sequence number is called
node1.
Temporarily mark the galera Pacemaker resource as unmanaged:
crm resource unmanage galera
Mark the node as bootstrap node (call the following commands from the
bootstrap node which is node1 in this example):
crm_attribute -N node1 -l reboot --name galera-bootstrap -v true
crm_attribute -N node1 -l reboot --name master-galera -v 100
Promote the bootstrap node:
crm_resource --force-promote -r galera -V
Redetect the current state of the galera resource:
crm resource cleanup galera
Return the control to Pacemaker:
crm resource manage galera
crm resource start galera
The MariaDB Galera Cluster is now running and Pacemaker is handling the cluster.