Creating a new hostgroup

You should have a working Nagios Core 4.0 or better server running with a web interface.

You should also have at least two hosts that form a meaningful group; perhaps they're similar kinds of servers, such as web servers, or are monitored by the same team, or both at a physical location.

In this example, we have two web servers, sparta.example.net and athens.example.net, and we're going to add them to a group called webservers.

We can add our new hostgroup webservers to the Nagios Core configuration as follows:

We should now be able to visit the Host Groups section of the web interface and see a new hostgroup with two members:

The preceding configuration that we have added includes a new file with a new hostgroup into the Nagios Core configuration and inserts appropriate hosts into the group. The hostgroup creates a separate section in the web interface for us to get a quick overview of only the hosts in that particular group.

The way we've added hosts to the preceding groups is actually not the only way to do it. If we prefer, we can instead name the hosts for the group inside the group definition, using the members directive, so we could have something like the following:

define hostgroup {
    hostgroup_name  webservers
    alias           Webservers with Greek names
    members         athens.example.net,sparta.example.net
}

We can also make a hostgroup that always includes every single host, if we find that useful:

define hostgroup {
    hostgroup_name  all
    alias           All hosts
    members         *
}

If we're going to be using hostgroups extensively in our Nagios Core configuration to add hosts to groups, we should use whichever of the two methods we think is going to be easiest for us to maintain.

It's worth noting that a host can be in more than one group and there is no limit on the number of groups we can declare, so we can afford to be quite liberal with how we group our hosts into any sort of useful categories. examples of hostgroups could be organizing servers by a function, manufacturer, or colocation customer or organizing routers by BGP or OSPF usage; it all depends on what kind of network we're monitoring.