Synnefo » snf-ganeti

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  <!ENTITY dhdate      "<date>June 08, 2010</date>">

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       allowed: see man(7), man(1). -->

  <!ENTITY dhsection   "<manvolnum>8</manvolnum>">

  <!ENTITY dhucpackage "<refentrytitle>ganeti-watcher</refentrytitle>">

  <!ENTITY dhpackage   "ganeti-watcher">

  <!ENTITY debian      "<productname>Debian</productname>">

  <!ENTITY gnu         "<acronym>GNU</acronym>">

  <!ENTITY gpl         "&gnu; <acronym>GPL</acronym>">

  <!ENTITY footer SYSTEM "footer.sgml">

]>

<refentry>

  <refentryinfo>

    <copyright>

      <year>2007</year>

      <year>2008</year>

      <year>2009</year>

      <year>2010</year>

      <holder>Google Inc.</holder>

    </copyright>

    &dhdate;

  </refentryinfo>

  <refmeta>

    &dhucpackage;

    &dhsection;

    <refmiscinfo>Ganeti 2.3</refmiscinfo>

  </refmeta>

  <refnamediv>

    <refname>&dhpackage;</refname>

    <refpurpose>Ganeti cluster watcher</refpurpose>

  </refnamediv>

  <refsynopsisdiv>

    <cmdsynopsis>

      <command>&dhpackage; </command>

      <arg><option>--debug</option></arg>

      <arg><option>--job-age=<replaceable>age</replaceable></option></arg>

      <arg><option>--ignore-pause</option></arg>

    </cmdsynopsis>

  </refsynopsisdiv>

  <refsect1>

    <title>DESCRIPTION</title>

    <para>

      The <command>&dhpackage;</command> is a periodically run script

      which is responsible for keeping the instances in the correct

      status. It has two separate functions, one for the master node

      and another one that runs on every node.

    </para>

    <para>

      If the watcher is disabled at cluster level (via

      the <command>gnt-cluster watcher pause</command> command), it

      will exit without doing anything. The cluster-level pause can be

      overriden via the <option>--ignore-pause</option> option, for

      example if during a maintenance the watcher needs to be disabled

      in general, but the administrator wants to run it just once.

    </para>

    <para>

      The <option>--debug</option> option will increase the verbosity

      of the watcher and also activate logging to the standard error.

    </para>

    <refsect2>

      <title>Master operations</title>

      <para>

        Its primary function is to try to keep running all instances

        which are marked as <emphasis>up</emphasis> in the configuration

        file, by trying to start them a limited number of times.

      </para>

      <para>

        Another function is to <quote>repair</quote> DRBD links by

        reactivating the block devices of instances which have

        secondaries on nodes that have been rebooted.

      </para>

      <para>

        The watcher will also archive old jobs (older than the age

        given via the <option>--job-age</option> option, which

        defaults to 6 hours), in order to keep the job queue

        manageable.

      </para>

    </refsect2>

    <refsect2>

      <title>Node operations</title>

      <para>

        The watcher will restart any down daemons that are appropriate

        for the current node.

      </para>

      <para>

        In addition, it will execute any scripts which exist under the

        <quote>watcher</quote> directory in the Ganeti hooks directory

        (@SYSCONFDIR@/ganeti/hooks). This should be used for

        lightweight actions, like starting any extra daemons.

      </para>

      <para>

        If the cluster

        parameter <literal>maintain_node_health</literal> is enabled,

        then the watcher will also shutdown instances and DRBD devices

        if the node is declared as offline by known master candidates.

      </para>

      <para>

        The watcher does synchronous queries but will submit jobs for

        executing the changes. Due to locking, it could be that the jobs

        execute much later than the watcher submits them.

      </para>

    </refsect2>

  </refsect1>

  <refsect1>

    <title>FILES</title>

    <para>

      The command has a state file located at

      <filename>@LOCALSTATEDIR@/lib/ganeti/watcher.data</filename>

      (only used on the master) and a log file at

      <filename>@LOCALSTATEDIR@/log/ganeti/watcher.log</filename>. Removal of

      either file will not affect correct operation; the removal of

      the state file will just cause the restart counters for the

      instances to reset to zero.

    </para>

  </refsect1>

  &footer;

</refentry>

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