fence device para maquinas virtuales Xen con RedHat Cluster

Suele ser útil montar un cluster virtual para el entorno de desarrollo tal como se explica en el resumen de la presentación que se hizo en Jornas Tècnicas RedIRIS 2007: Virtualización y alta disponibilidad para entornos de hospedaje y desarrollo de portales web.

Si se hace con Xen y se quiere ser lo más realista posible, lo mejor sería definir también los fence devices, que són los encargados de reiniciar un nodo si se ha quedado “frito”.

En la red podeis encontrar un script llamado fence_xen, que lo que hace es conectarse a la maquina física (donde estan las maquinas virtuales) y forzar el reinicio del nodo del mismo modo que lo haría una iLO de HP o una DRAC de Dell.

Este script ha dejado de funcionar para las versiones nuevas de RedHat Cluster, por lo que aquí teneis una modificación de éste para que funcione en RedHat 5 (y las Fedoras con versión igual o superior a la 7):

fence_xen

#!/usr/bin/perl
##
##  Copyright (C) 2005 Red Hat, Inc.  All rights reserved.
##
##  This copyrighted material is made available to anyone
##  wishing to use, modify, copy, or redistribute it subject
##  to the terms and conditions of the
##  GNU General Public License v.2.
##

use Getopt::Std;

# Get the program name from $0 and strip directory names
$_=$0;
s/.*\///;
my $pname = $_;

# Default is to use ssh for connection to the host
# for this to be effective you'll need to have an ssh key on the
# VMs that can log in to the host without a passphrase.
# If you device to use rsh then you'll need to
# edit /root/.rhosts
#
# Also note that you'll need to set /proc/sys/kernel/sysrq to "1"
# in the VMs for this to work at all.
#
$opt_c = "ssh";
$opt_u = "root";

# WARNING!! Do not add code bewteen "#BEGIN_VERSION_GENERATION"
# and "#END_VERSION_GENERATION"  It is generated by the Makefile

#BEGIN_VERSION_GENERATION
$FENCE_RELEASE_NAME="DEVEL.1105353156";
$REDHAT_COPYRIGHT=("Copyright (C) Red Hat, Inc.  2005  All rights
reserved.");
$BUILD_DATE="(built Mon Jan 10 10:35:41 GMT 2005)";
#END_VERSION_GENERATION

sub usage
{
   print "Usage:\n";
   print "\n";
   print "$pname [options]\n";
   print "\n";
   print "Options:\n";
   print "  -h               This help message\n";
   print "  -s           IP address or hostname of host system\n";
   print "  -d       Domain name of system to fence\n";
   print "  -u         User name (default root)\n";
   print "  -c          Command to log into host (default ssh)\n";

   exit 0;
}

sub fail
{
   ($msg)=@_;
   print $msg."\n" unless defined $opt_q;

   if (defined $t)
   {
      # make sure we don't get stuck in a loop due to errors
      $t->errmode('return');

      logout() if $logged_in;
      $t->close
   }
   exit 1;
}

sub fail_usage
{
   ($msg)=@_;
   print STDERR $msg."\n" if $msg;
   print STDERR "Please use '-h' for usage.\n";
   exit 1;
}

sub version
{
   print "$pname $FENCE_RELEASE_NAME $BUILD_DATE\n";
   print "$SISTINA_COPYRIGHT\n" if ( $SISTINA_COPYRIGHT );
   exit 0;
}

sub get_options_stdin
{
   my $opt;
   my $line = 0;
   while( defined($in = <>) )
   {
      $_ = $in;
      chomp;

      # strip leading and trailing whitespace
      s/^\s*//;
      s/\s*$//;

      # skip comments
      next if /^#/;

      $line+=1;
      $opt=$_;
      next unless $opt;
      ($name,$val)=split /\s*=\s*/, $opt;

      if ( $name eq "" )
      {
         print STDERR "parse error:illegal name in option $line\n";
         exit 2;
      }
      # DO NOTHING -- this field is used by fenced
      elsif ($name eq "agent" )
      {
      }
      elsif ($name eq "host" )
      {
         $opt_s = $val;
      }
      elsif ($name eq "nodename" )

      {
         $opt_d = $val;
      }
      elsif ($name eq "user" )
      {
         $opt_u = $val;
      }
      elsif ($name eq "cmd" )
      {
         $opt_c = $val;
      }
      # Maybe password...
      # Excess name/vals will fail
      else
      {
         fail "parse error: unknown option \"$opt\"";
      }
   }
}

### MAIN #######################################################
if (@ARGV > 0) {
   getopts("hs:d:u:c:vV") || fail_usage ;

   usage if defined $opt_h;
   version if defined $opt_V;

   fail_usage "Unknown parameter." if (@ARGV > 0);
   fail_usage "No '-d' flag specified." unless defined $opt_d;
   fail_usage "No '-s' flag specified." unless defined $opt_s;

   } else {
      get_options_stdin();

      fail "failed: no host system name" unless defined $opt_s;
      fail "failed: no domain to fence" unless defined $opt_d;
   }

exit system ("$opt_c -l $opt_u $opt_s xm sysrq $opt_d b");