Nagios dual check
~~~~~~~~~~~~~~~~~
2012.03.04. Still in experimental state!
2012.03.15. Version: 0.2, source modifications (see the repo), Nagios config examples

Files:
  check_dual.pl

Description:
	It is often necessary to run checks for a host with dual IP address. The
	check_dual.pl is an attempt to simplify this task. The Nagios config is allow
	us to write anything in a 'define host' 'address' directive. Let's write both
	addresses separated by comma and similarly to the check_nrpe stanza, use the
	check_dual and check_dual_1 commands as described below.

  # commands
	define command {
		command_name		check_dual
		command_line		$USER1$/check_dual.pl -H $HOSTADDRESS$ -c $ARG1$ -- $ARG2$ $ARG3$ $ARG4$ $ARG5$ $ARG6$ $ARG7$ $ARG8$ $ARG9$ 
	}

	define command {
		command_name		check_dual_1
		command_line		$USER1$/check_dual.pl -H $HOSTADDRESS$ -1 -c check_nrpe -- -c $ARG1$ $ARG2$ $ARG3$ $ARG4$ $ARG5$ $ARG6$ $ARG7$ $ARG8$ $ARG9$ 
	}
  ...
  # dual host template
	define host {
		use									generic-host
		name								dual-host
		check_command				check_dual!check_ping!-w!3000.0,50%!-c!5000.0,70%!-p!5
		register						0
	}
  ...
  # host definition
	define host {
		use             dual-host,host-pnp
		host_name				xxxxx
		address					10.134.68.7,10.134.69.7
	}        
  ...
  # dual check definition
	define service {
		host_name						xxxxx
		service_description	SSH
		check_command		    check_dual!check_ssh
	}
  # single check definition
	define service {
		host_name						xxxxx
		service_description	users
		check_command		    check_dual_1!check_users
	}

	check_dual.pl itself contains two truth table to calculate the resulting
	state. There are two kind of checks:
		'one of two' - usually nrpe checks ('-1' command line args), these checks
									 are ok even if they can be done through only one of the ip
									 addresses. eg. check_nrpe!check_disk
		'two of two' - check on both ip address should be ok. eg. check_ping of the
		               hosts's ip addresses.
  See the truth tables in check_dual.pl source.

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