Using Nagios to monitor "service-less" hosts

[Fermín Galán Márquez]

Dear Andy,

>>> Is that right? Why don't fully decouple host-monitoring from service
monitoring?
>
> No.  Nagios does use the check-host-alive command to determine if the host
is up - and, yes, hosts and services are separate in that a 
> host doesn't have to have any services, but a service must have a host.
>
> I have 2 hosts which are actually 2 gateway routers, which do not have any
corresponding services.  Nagios issues a warning saying they 
> don't have any services associated on every startup, but it monitors them
perfectly.  Even if they drop off the network for a few 
> seconds, Nagios knows about it.  This is through the use of check_ping as
the check-host-alive command - however, on one of my previous 
> servers, the gateway router blocked ICMP, so I used check_ssh as the
check-host-alive command which also worked perfectly.

Your looking glass is very clarifiying. Thanks! :)

> It sounds as if you don't have active checks enabled for the hosts.  The
error "Not enough data..." means an active or passive check 
> hasn't been submitted for the host yet.

I cann't locate active or passive checks directives related with hosts in
the documentation
(http://nagios.sourceforge.net/docs/1_0/xodtemplate.html#host). However,
there is such directives related with services, in particular
active_check_enabled and passive_check_enabled
(http://nagios.sourceforge.net/docs/1_0/xodtemplate.html#service). However,
I have checks_enabled directive in the hosts activate. Also note there is
not equivalents to normal_check_interval or retry_check_interval (for
services) in host objects (apparently). 

Maybe I'm using a too old Nagios release? I'm using 1.4-2 but I've seen the
most recent one is 2.5.

I think it would be very clarifying if you could show me the hosts.cfg
fragment you are using for FH_Gateway and SC_Gateway in your looking glass,
please.

As reference, the fragment from hosts.cfg that I'm using:

# Generic host definition template
define host{
        name                            generic-host    ; The name of this
host template - referenced in other host definitions, used for tem
plate recursion/resolution
        notifications_enabled           1       ; Host notifications are
enabled
        event_handler_enabled           0       ; Host event handler is
disabled
        flap_detection_enabled          0       ; Flap detection is disabled
        process_perf_data               1       ; Process performance data
        retain_status_information       1       ; Retain status information
across program restarts
        retain_nonstatus_information    1       ; Retain non-status
information across program restarts

        register                        0       ; DONT REGISTER THIS
DEFINITION - ITS NOT A REAL HOST, JUST A TEMPLATE!
        }
define host{
        use                     generic-host            ; Name of host
template to use
        host_name               nagios-test
        alias                   NAGIOS Test
        address                 192.168.1.112
        parents                 gw
        check_command           check-host-alive
        checks_enabled          1
        max_check_attempts      20
        notification_interval   60
        notification_period     24x7
        notification_options    d,u,r
        }

Thanks again!

Best regards,

--------------------
Fermín Galán Márquez
CTTC - Centre Tecnològic de Telecomunicacions de Catalunya
Parc Mediterrani de la Tecnologia, Av. del Canal Olímpic s/n, 08860
Castelldefels, Spain
Room 1.02
Tel : +34 93 645 29 12 
Fax : +34 93 645 29 01
Email address: fermin.galan at cttc.es 


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