check the master/slave status

[pyh at mail.nsbeta.info]

I wrote a nagios plugin for monitoring the status of master/slave DNS.
Just to check if their serial number is the same. The script shows 
below,thanks for all your directions. 

#!/usr/bin/perl
use strict;
use Net::DNS;
use Getopt::Std; 

my %opts;
getopts('hm:s:z:', \%opts);
if ($opts{'h'}) {
    usage();
}
my $master = $opts{'m'} || usage();
my $slave = $opts{'s'} || usage();
my $zone = $opts{'z'} || usage(); 

my $s1 = qrsoa($master,$zone);
my $s2 = qrsoa($slave,$zone); 

if ($s1 != -1 && $s1 == $s2) {
    print "OK\n";
    exit 0;
} else {
    print "CRITICAL: zone game.yy.com sync error\n";
    exit 2;
} 


sub qrsoa {
    my $host = shift;
    my $zone = shift;
    my $res   = Net::DNS::Resolver->new(nameservers => [$host]);
    my $query = $res->query($zone, "SOA");
    return $query ? ($query->answer)[0]->serial : -1;
} 

sub usage {
    print <<EOF;
    Usage: $0 -m 8.8.8.8 -s 8.8.4.4 -z example.com
    -m  master DNS ip or name
    -s  slave DNS ip or name
    -z  zone name
    -h  show this help page
EOF
    exit 0;
}