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

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

In this example, we have three servers performing mail functions: smtp.example.net, pop3.example.net, and imap.example.net, running an SMTP, POP3, and IMAP daemon, respectively. All three of the hosts are set up in Nagios Core, and so are their services. We're going to add them into a new servicegroup called mailservices.

Here are the definitions of the hosts and services used in this example, so you can see how everything fits together:

define host {
    use                 linux-server
    host_name           smtp.example.net
    alias               smtp
    address             192.0.2.31
    hostgroups          webservers
}
    define service {
        use                  generic-service
        host_name            smtp.example.net
        service_description  SMTP
        check_command        check_smtp
    }
define host {
    use                 linux-server
    host_name           pop3.example.net
    alias               pop3
    address             192.0.2.32
    hostgroups          webservers
}
    define service {
        use                  generic-service
        host_name            pop3.example.net
        service_description  POP3
        check_command        check_pop
    }
define host {
    use                 linux-server
    host_name           imap.example.net
    alias               imap
    address             192.0.2.33
    hostgroups          webservers
}
    define service {
        use                  generic-service
        host_name            imap.example.net
        service_description  IMAP
        check_command        check_imap
    }

We can add our new servicegroup with the following steps:

We should now be able to visit the Service Groups section of the web interface and see a new servicegroup with three members:

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

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

define servicegroup {
    servicegroup_name  mailservices
    alias              Mail services
    members            smtp.example.net,SMTP,pop3.example.net,POP3,imap.example.net,IMAP
}

Note that we need to specify both the host that the service is on and the services to be monitored on it. This string needs to be comma-separated. The hostname always comes first, but it can be followed by any number of its services that are to be monitored.

This allows us to make a servicegroup that always includes every single service on every host, if we find that useful:

define servicegroup {
    servicegroup_name  all
    alias              All services
    members            *
}

If we're going to use servicegroup definitions extensively in our Nagios Core configuration to add services 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 service 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 services into any sort of useful categories. A few examples of this could be organizing services by the appropriate contact for their notifications, internal functions, or customer-facing functions.