On Centos 7 installs the systemd zabbix-agent.service and zabbix-server.service fails to start after a reboot. Reason: network bindings are not ready to use.

Solution: for the zabbix-agent.service

[Unit]
Description=Zabbix Monitor Agent
#After=syslog.target network.target
After=syslog.target network.target network-online.target

[Service]
Type=forking
ExecStart=/usr/sbin/zabbix_agentd
User=zabbix
PIDFile=/run/zabbix/zabbix_agentd.pid

[Install]
WantedBy=multi-user.target
~

Allow to start zabbix(agent&server) after network is ready. Add systemd dependancy "network-online.target" in the *.service.