Why separate hosts and services

Andreas Ericsson ae at op5.se
Thu Apr 15 16:24:14 CEST 2004


Chris Wilson wrote:
> Why is it that Nagios has separate concepts of hosts and services? Since
> the only way to check that a host is up is to query some service on it,
> why bother with hosts at all? Why not just consider a host to be the sum
> of the service(s) that it implements, depending on one another and on
> other host-services? Please could someone explain the rationale to me?
> 
I can think of at least two good reasons.
1) Problem localisation. When a service fails, someone has to fix it. If 
they don't know what machine it's on the purpose of a monitoring system 
is soundly defeated.
Ofcourse, you could type in the host_address and host_alias in every 
service-description, but keeping things the way they are really saves a 
lot of typing compared to that.

2) Notification suppression. If a service fails, nagios immediately 
checks if the host is down. If it is, no more service checks will be 
scheduled until the host pops back up.

> Also, I had an idea about grouping services together into meta-services or
> super-services. One can imagine that if a service provided by a router is
> "packet forwarding", the best way to determine if this service is up or
> down is to examine the hosts (or services :-) below it. If they are all
> down then packet forwarding is obviously down as well, and we should only 
> get one notification.
> 
> Is there any way to configure this with Nagios? If so, then I apologise
> for not asking the users list, but I have never seen such a facility. If
> not, would it be difficult to add?
> 
Check out (host- and service-) dependancies. It's all properly documented.

> Cheers, Chris.

-- 
Mvh / Best Regards
Sourcerer / Andreas Ericsson
OP5 AB
+46 (0)733 709032
andreas.ericsson at op5.se


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