Checking whether a service is available over a network can be done from a single machine. In such cases, using a single dedicated machine to do all of these checks would be a good idea as it also reduces the burden and load to be on just a single computer on your network. In reality, this is not enough for a robust computer and failure monitoring solution.

In many cases, performing checks on machines other than the Nagios server is a necessity. this is the case for the simplest tasks, such as making sure you have enough storage space on a database server. It is also needed for more complex checks such as monitoring the load of machines and being able to react to unbalanced loads across machines. Nagios offers ways to do these types of checks and to set them up in an easy manner. Depending on what the critical issues are for your network, the choice is usually to either use SSH or NRPE to perform the checks on other machines.

The first is easier to set up from a network and administrative...