Empty hostgroup check in the configuration arbitrary or limitation in nagios core ?

[Andreas Ericsson]

L B wrote:
> Hello,
> 
> I have many nagios servers for different regions in the world, and I
> want to create a standard installation with a set of hostgroups,
> commands, and services with default thresholds, for all my Nagios
> admins. My services are applied to hostgroups, and I want to add a
> check to a host only by adding this host to the relevant hostgroup.
> 
> Example :
>  - I define a command check_dns
>  - I define a hostgroup dns-server-hostgroup
>  - I define a service check_dns applied to dns-server-hostgroup
> 
> Then I define a host, and if it's a DNS server, I add it to the DNS
> hostgroup (I'm running Nagios 3):
> define host {
> ....
> hostgroups  +dns-server-hostgroup
> }
> 
> This works very well in my configuration except that if I install a
> nagios server in a new region, and they not have for example a NFS
> server, I will get an error because nfs-server-hostgroup is empty. I
> fixed this by adding "register 0" to the service definition, but that
> means the admins have to comment out this line to enable the check on
> the hostgroup.
> 
> So I would like to be allowed to create checks on empty hostgroups,
> and of course if the hostgroup is empty, no check is done.
> 
> Is there something technically in the nagios core that prevents
> creating empty hostgroups

No, but when a service is assigned to a hostgroup, that hostgroup
is already expanded (and found to contain zero hosts), so the service
is assigned to no host at all, but still doesn't have "register 0"
in it, so it's a faulty service.

> or is it an arbitrary configuration check
> because it's assumed that a user probably doesn't want to check a
> service on a empty hostgroup ?
> 
> I find this configuration approach very convenient so I hope it's the
> second answer ! :-)
> 

It's a bit of both actually. You'd need to submit a patch to get Nagios
to accept services linking to empty hostgroups though.

-- 
Andreas Ericsson                   andreas.ericsson at op5.se
OP5 AB                             www.op5.se
Tel: +46 8-230225                  Fax: +46 8-230231

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