Frontend shows:

Database error

The frontend does not match Zabbix database. Current database version (mandatory/optional): 0/0. Required mandatory version: 3000000. Contact your system administrator.

while db is:

MariaDB [zabbix]> select * from dbversion;
ERROR 1047 (08S01): WSREP has not yet prepared node for application use

MariaDB [zabbix]> select now();
ERROR 1047 (08S01): WSREP has not yet prepared node for application use

Would be good if frontend message technically will be more correct.

p.s. Galera cluster requires 3 nodes normally as minimal number. If 2 nodes, from those 3, are offline, the single alive node will reply with the error.