$HOSTNAME$ in commands? (Was: Re: Monitoring a matrix of load-balanced VirtualHosts?)

[Andreas Ericsson]

Chris Wilson wrote:
> Hi JB,
> 
> 
>>I've been told to check '{machinename}.foo.com', but - according to
>>docs/macros.html - I can't use $HOSTNAME$ or $HOSTALIAS$ in either
>>host or service checks.
>>
>>My 1st instinct is to do just that - something like
>>        check_command           check_lb_vhost!$HOSTNAME$.foo.com
>>
>>but it seems I can't. This is more than a bit annoying, and seems a
>>very odd design decision. I can't be the only one who wants this
>>functionality.
> 
> 
> I agree that that is very odd. The information must be available, and
> you could probably patch Nagios to make those macros work.
> 
> Looking at the source code, it should work now. base/checks.c grabs all
> macros for hosts and services before running the check. The only problem
> might be the nesting of macros, which I haven't tried and don't know if
> it works. You could try this:
> 

It's for this precise reason that it doesn't work. $HOSTNAME$ is 
translated to $ARG1$ in the above example. $ARG1$ is properly expanded 
and $HOSTNAME$ (which is an invalid shell variable) is passed to 
popen(3) as is, and subsequently dropped by the shell.

> 	define service {
>                 use                     vhost-service
>                 service_description     $HOSTNAME$.bar.com
>                 check_command           my_check_http_on_host!bar.com
>                 hostgroup_name          bar_com_servers
>         }
>         
>         define command {
>                 command_name    my_check_http_on_host
>                 command_line    $USER1$/check_http -I $HOSTADDRESS$ -H
>         $HOSTNAME$.$ARG1$
>         }
> 

This will work, because it isn't nested anymore (although 
$HOSTNAME$.$ARG1$ could just as easily be replaced by 
$SERVICEDESCRIPTION$ or whatever that macro is called).

> If not, let me know (with details about exactly what happens when you
> try) and I'll have another look. Or maybe a higher guru will.
> 
> Cheers, Chris.

-- 
Andreas Ericsson                   andreas.ericsson at op5.se
OP5 AB                             www.op5.se
Lead Developer


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