NAME
    OpenMosix::HA -- High Availability (HA) layer for an openMosix cluster

SYNOPSIS
      use OpenMosix::HA;

      my $ha = new OpenMosix::HA;

      # spawn all apps for resource group "foo", runlevel "run"
      $ha->tell("foo","run");

      # spawn all apps for resource group "foo", runlevel "runmore"
      # (this stops everything started by runlevel "run")
      $ha->tell("foo","runmore");

      # get status of all resource groups
      $ha->status();

DESCRIPTION
    This module provides basic "init" functionality, giving you a single
    inittab-like file to manage daemon startup and restart across a cluster
    of openMosix machines.

    This gives you a high-availability cluster with low hardware overhead.
    In contrast to traditional HA clusters, we use the openMosix cluster
    membership facility to provide heartbeat and to detect network
    partitions.

    All you need to do is build a relatively conventional openMosix cluster,
    install this module, and configure it to start and manage your HA
    processes. There is no need to use the heartbeat serial cables, spare
    ethernet cards, or high-end server machines which traditional HA
    requires. There is no need for chained SCSI buses -- you can share disks
    among many nodes via any number of other current technologies, including
    SAN, NAS, GFS, or Firewire (IEEE-1394).

BACKGROUND
    Normally, a process-migration-based cluster computing technology (such
    as openMosix) is orthogonal to the intent of high availability. When
    openMosix nodes die, any processes migrated to those nodes will also
    die, regardless of where they were spawned. The higher the node count,
    the more frequently these failures are likely to occur.

    But if processes are started via OpenMosix::HA, any processes and
    resource groups which fail due to node failure can be configured to
    automatically restart on other nodes. OpenMosix::HA detects process
    failure, selects a new node out of all currently available, and
    deconflicts the selection so that two nodes don't restart the same
    process or resource group.

    In addition to the normal inittab format, the configuration file for
    OpenMosix::HA includes an extra "resource group" column -- this is what
    enables you to group processes, disk mounts, virtual IP addresses, and
    related resources into resource groups.

    Any given node only needs to be able to support a subset of all resource
    groups. OpenMosix::HA provides an extra "test" runmode (beyond init's
    normal 'wait', 'once', and 'respawn'), enabling the module to
    automatically test a given node for fitness before considering starting
    a given resource group there.

    There is no "head" or "supervisor" node in an OpenMosix::HA cluster --
    there is no single point of failure. Each node makes its own
    observations and decisions about the start or restart of processes and
    resource groups.

    IO Fencing (also STOMITH or STONITH, the art of making sure that a
    partially-dead node doesn't continue to access shared resources) can be
    handled as it is in conventional HA clusters, by a combination of
    exclusive device logins when using Firewire, distributed locks when
    using GFS or other SAN, and brute-force methods such as X10 or
    network-controlled powerstrips. OpenMosix::HA provides a callback hook
    which can be used to trigger the latter.

AVAILABILITY
    This module is based on my IS::Init module, which is already in
    production and available from CPAN. My wife and I had hoped to have a
    beta version of OpenMosix::HA available by the time of Moshe Bar's Feb 5
    2003 openMosix talk at the Silicon Valley Linux Users Group.

    Then I unexpectedly became involved in data collection for Columbia's
    California transit -- SVLUG member Ian Kluft was one of the few
    witnesses. We decided it best to defer work on this module in favor of
    improving our understanding of where the shuttle's breakup actually
    began, relaying our results to Johnson Space Center and working with
    media to encourage others to do the same. These efforts by ourselves and
    others have been successful beyond what any of us expected -- NASA JSC
    emergency ops responded to us personally and as of this writing a search
    in California is already underway. But I don't have a Perl module for
    you yet.

    For a production version of OpenMosix::HA, check CPAN.org,
    TerraLuna.Org, or Infrastructures.Org in early March 2003, or contact
    me. Beta versions will become available as time permits before then.

AUTHOR
            Steve Traugott
            CPAN ID: STEVEGT
            stevegt@TerraLuna.Org
            http://www.stevegt.com

COPYRIGHT
    Copyright (c) 2003 Steve Traugott. All rights reserved. This program is
    free software; you can redistribute it and/or modify it under the same
    terms as Perl itself.

    The full text of the license can be found in the LICENSE file included
    with this module.

SEE ALSO
    IS::Init, openMosix.Org, qlusters.com

