Using Nagios to monitor "service-less" hosts

[Andy Shellam (Mailing Lists)]

Thanks for that Robert, that could explain things, and this rings a very 
faint bell in my mind back when I originally set Nagios up.

I set regular host checks up because there are currently 5 minutes 
between service checks, and if this is the only time that a host gets 
checked, then if a gateway goes down, I won't know about it for at most 
5 minutes (or never if it doesn't check services.)  But equally I don't 
want to be hitting my mail, web and database services with a full 
transaction/query/request every minute - so 5 minutes per service is 
perfect.

Personally I've not noticed any performance decrease having host checks 
set - it's on a moderately spec'd server, and if a gateway does go down, 
I know about it almost immediately and can take action.

JOOI, why is it said that a host check degrades performance?  All it's 
doing is running a command like a service?  Sure, if the host check 
comes back that it's down, then it has to walk the parent tree to find 
any network blockages, but when everything's all up and running, surely 
there's nothing more to do?

Andy.

Sloane, Robert Raymond wrote:
>> Host definition for SC-Gateway:
>> --------------------------------------------------------------
>> ----------------
>> define host {
>>     check_interval            1
>>     
>
> You might want to look at the documentation for the check_interval
> directive for host objects.  It says:
>
> NOTE: Do NOT enable regularly scheduled checks of a host unless you
> absolutely need to! Host checks are already performed on-demand when
> necessary, so there are few times when regularly scheduled checks would
> be needed. Regularly scheduled host checks can negatively impact
> performance - see the performance tuning tips for more information. This
> directive is used to define the number of "time units" between regularly
> scheduled checks of the host. Unless you've changed the interval_length
> directive from the default value of 60, this number will mean minutes.
> More information on this value can be found in the check scheduling
> documentation.
>
> and there is a link to performance tuning tips that says:
>
> Don't schedule regular host checks. Do NOT schedule regular checks of
> hosts unless absolutely necessary. There are not many reasons to do
> this, as host checks are performed on-demand as needed. To disable
> regular checks of a host, set the check_interval directive in the host
> definition to 0. If you do need to have regularly scheduled host checks,
> try to use a longer check interval and make sure your host checks are
> optimized (see above).
>   


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