ERROR listener failed: zbx_tcp_listen() fatal error: unable to serve on any address [[-]:10051]

Load testing scenario and similar error to the post below, but different reason.

Zabbix runs as part of Pacemaker cluster.

There were 2 reasons:

1. mySQL did not have enough connections allowed
Set this parameter in my.cnf: max_connections = 512

2. Zabbix service controlled by Pacemaker. This requires maintenance mode. I saw articles on how to do it with crm command but this is obsolete. So here is how with pcs

pcs property set maintenance-mode=true

pcs property set maintenance-mode=false

Once it is in maintenance mode, it can controlled independently of Pacemaker.