Exploding check commands batman ...

[Gavin Carr]

On Fri, Jul 01, 2005 at 09:28:45PM +0200, Andreas Ericsson wrote:
> I was thinking along the lines of this;
> 
> command_name  check_foo_command
> command_line  check_foo -H $HOSTADDRESS$ -C "$ARG1$" -p "$ARG2$"
> 
> Where check_foo is a plugin written in perl that checks something via 
> SNMP. It's reasonable to assume that most will want to give the 
> community as an argument from the service-object, while most want to use 
> the default port.
> 
> Nagios will translate all 32 $ARGx$ macros even if some aren't set 
> (which is a bit weird, but useful for this purpose) and simply remove 
> the macro-tags since their counterparts will be NULL pointers (as 
> opposed to null strings).
> 
> So, the resulting command turns out to
> 
> check_foo -H host -C bar -p ""
> 
> which means the imaginary variable $port will be set to the null-string 
> and thus it will be defined but will evaluate to false when being 
> evaluated as a boolean expression, as it would have if it wasn't 
> specified at all.

That's a nice idea Andreas. So are you adding the boolean testing to the 
current nagios plugin infrastructure?

The only real negative is that you're then likely to use check commands
with more options, and because we're using positional arguments you're
likely to end up with lots of empty placeholders e.g.

  check_command   check_http!/foo/bar.html!!!!!404

etc.

A nasty example of this is things like check_by_ssh checks, where your 
arguments are typically on the inner command rather than the other 
check_by_ssh one e.g.

  command_line    $USER1$/check_by_ssh -4 -H $HOSTADDRESS$ -t 20 -C '/usr/lib/nagios/plugins/check_disk -w $ARG1$ -c $ARG2$ -l'
  command_line    $USER1$/check_by_ssh -4 -H $HOSTADDRESS$ -t 20 -C '/usr/lib/nagios/plugins/check_swap -w $ARG1$ -c $ARG2$'

I've got 10 or so of these tests defined, and now have a host that is
listening on a non-standard ssh port. Adding a '-p "$ARG1$"' to the 
check_by_ssh is doable, of course, but it necessitates an empty first 
argument for all test on hosts with standard ssh ports, which is a bit
ugly too. 

Anyone think of an elegant way to handle this?

Cheers,
Gavin



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