3 Agent - Zabbix
https://www.zabbix.com/documentation/2.2/manual/concepts/agentZabbix agents are extremely efficient because of use of native system calls for gathering statistical information. Passive and active checks. Zabbix agents can perform passive and active checks. In a passive check the agent responds to a data request. Zabbix server (or proxy) asks for data, for example, CPU load, and Zabbix agent sends back the ...
3 Agent 2 - Zabbix
https://www.zabbix.com/documentation/5.0/manual/concepts/agent2Agent 2 is written in Go (with some C code of Zabbix agent reused). A configured Go environment with a currently supported Go version is required for building Zabbix agent 2. Agent 2 does not have built-in daemonization support on Linux; since Zabbix 5.0.4 it can be run as a Windows service. Passive checks work similarly to Zabbix agent.