checkhostalive vs ping service

[Marc Powell]

On Oct 31, 2008, at 5:10 AM, L B wrote:

> Hello all,
>
> What is the difference between checking a host is alive with a check
> in the host template (check_command check-host-alive), and creating a
> ping service applied to the host ?

If the host check returns a non-OK state, notifications for services  
on that host are suppressed. If the host is specified as a parent to  
another host that is also unavailable, the second host is put in an  
UNREACHABLE state as opposed to a DOWN state.

> I did a test with both configurations, and didn't see a different  
> behavior.
>
> I thought it was a question of dependencies: if a service fails, a
> host check is done to check if the host is up. But if one of the
> services (ping or another) fails, a host check is done anyway even if
> my host checks are disabled (check_interval 0), (that's a correct
> behavior for me)

Yes. Using check_interval 0 disables regularly scheduled host checks.  
They'll still be checked on an as-needed basis unless you change the  
check_period, disable active checks or do not specify a check_command  
(I don't do host checks by using all three of these methods).

> My configuration doesn't have host checks because it was imported
> from Nagios 2.x, and disabling host checks was an optimization setting

Same here.

> I've read somewhere (I also read that it's not necessary anymore with
> nagios 3) . Now I'm running Nagios 3, so I'm wondering if it would
> make sense to disable the ping service checks and do it as a host
> check. Why should I do /don't do this ?

If you like the suppression of notifications for services on down  
hosts or would like to use the parenting/reachability logic, host  
checks would be necessary.

I personally haven't decided if I will enable host checks. For the  
vast majority of our devices, we just ping them so it would be a  
redundant check and an additional object to Acknowledge when there's a  
problem. I would find them much more useful if the CGI's took  
advantage of the parenting with regard to Acks, etc... I'd like to be  
able to acknowledge a down host and have that same acknowledgement  
propagate down to it's services and to all it's child hosts and  
services but that's a different issue =)

--
Marc

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