Zabbix is an enterprise-level, open source (it's licensed under the GPL v. 2) monitoring software for both networks and applications. One Zabbix server can monitor hundreds of devices, and Zabbix can automatically discover servers and network devices. It is capable of monitoring services without installing any software on the monitored server, but you can also install agents on hosts that will collect data such as CPU load, memory, network, and disk utilization on behalf of the Zabbix server.
pfSense has packages for the Zabbix agent and Zabbix proxy, so you can install the agent or the proxy or both. The difference between the two is that while a Zabbix agent simply collects data from a local host and sends it to the Zabbix server, a Zabbix proxy can monitor remote hosts, collect performance and availability data, and offload the Zabbix server. Thus, it can perform many of the functions that the Zabbix server would otherwise have to do. In fact, it is somewhat easier to list the things a Zabbix proxy cannot do:
- A proxy cannot calculate triggers
- A proxy cannot process events
- A proxy cannot send alerts
- A proxy cannot execute remote commands
Most other functions that a Zabbix server can perform, such as Zabbix agent checks, built-in web monitoring, network discovery and low-level discovery (which is a way of automatically creating items, triggers, and graphs for devices as they are discovered) can be done by a Zabbix proxy. Also, if there's a firewall between the agents and the Zabbix server, having a single Zabbix proxy collect data from the agents makes configuration easier, as you only need to create one firewall rule to allow traffic between the Zabbix server and the proxy.
Zabbix agent and Zabbix proxy configuration are similar. Installing them adds items to the Services menu called Zabbix Agent MajorNumber.MinorNumber and Zabbix Proxy MajorNumber.Minor Number. As of this writing, the latest version of Zabbix is 3.4. In both configuration pages, there are fields where you can enter a list of Zabbix servers, as well as a list of Zabbix servers and ports for active checks. You can also set a Listen IP if you will be listening for a Zabbix server connection on a specific interface; the default is 0.0.0.0, which will cause pfSense to listen on all interfaces. You can also set the Listen Port.
Both the agent and proxy configuration have a section called TLS-RELATED Parameters. These settings control how the agent should send data to the proxy or server: either Unencrypted, with TLS and a pre-shared key (psk) or with TLS and a certificate (cert). You can also control what connections the agent or proxy will accept, with the same options. There are also options to select a certificate authority (TLS CA), a certificate (TLS Cert), and a text box where you can enter a pre-shared key (TLS PSK).
The one significant difference between Zabbix agent and proxy configuration is that the proxy configuration page has a section called SNMP Trap Monitoring which enables you to start the SNMP trapper process on the proxy. You can also specify a temporary file to be used for passing SNMP trap data from the SNMP daemon to the proxy in the SNMP Trapper File field.
There are several versions of both the Zabbix agent and proxy available on the packages list, presumably so administrators can make a suitable trade-off between stability and functionality. Installing and configuring Zabbix may be overkill, especially if you are setting up a network for home or a small office/home office, but if you need to administer a large network with no local administrators, Zabbix provides an easy way of centralizing host monitoring.