How do I choose whether to use an agent for monitoring or not?
The non-agent method is the preferred method for monitoring because it is the quickest and easiest to implement—and does not require the installation of software on customer hardware.
There are two requirements to utilize the non-agent monitoring option:
- System resources can only be monitored without an agent if the server is Unix-based (i.e. Linux, Solaris, FreeBSD, or Mac OS X). You can still monitor system resources on Windows, but the agent is required.
- The necessary port(s) must be open in the firewall. The port number varies depending on what is being monitored. For example, port 22 (SSH) is needed for monitoring system resource information, port 3306 for MySQL, etc. Consult the monitoring documentation for details about your specific server.
What you should see
The image on the right shows an example of how monitoring system resources with SSH works architecturally. Any other services being monitored (i.e. databases, application servers, network devices, etc.) will have to have corresponding ports in the firewall opened.
There are specific cases when using an agent is required for monitoring. The two primary reasons for needing to monitor via agent are: (1) the operating system to be monitored is Windows-based or (2) the servers being monitored are behind a firewall and cannot be accessed externally via direct port access. No inbound ports need to be opened to support this monitoring method, but ports 80 or 443 (HTTP/HTTPS) must be opened outbound from the firewall.
Two approaches for using the agent are possible. The agent can be installed on each server being monitored (see Figure 2). This is best in cases where there are just a few servers that require monitoring—or if the servers to be monitored are all Windows-based.
An alternative to installing an agent on each server is to install a single agent behind the firewall and have that agent monitor the other servers (see Figure 3). That agent monitors the other servers behind the firewall via the ports required for those services. Figure 3 shows an example of using SSH to monitor system resources on two servers. This approach is used in cases where a large number of servers need to be monitored during a test. It saves time since an agent does not have to be installed on each server.