en-US/ha-for-hosts.xml

<?xml version='1.0' encoding='utf-8' ?>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!ENTITY % BOOK_ENTITIES SYSTEM "cloudstack.ent">
%BOOK_ENTITIES;
]>

<!-- Licensed to the Apache Software Foundation (ASF) under one
    or more contributor license agreements.  See the NOTICE file
    distributed with this work for additional information
    regarding copyright ownership.  The ASF licenses this file
    to you under the Apache License, Version 2.0 (the
    "License"); you may not use this file except in compliance
    with the License.  You may obtain a copy of the License at
    
    http://www.apache.org/licenses/LICENSE-2.0
    
    Unless required by applicable law or agreed to in writing,
    software distributed under the License is distributed on an
    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
    KIND, either express or implied.  See the License for the
    specific language governing permissions and limitations
    under the License.
-->
<section id="ha-for-hosts">
  <title>HA for Hosts</title>
  <title>Dedicated HA Hosts</title>
  <para>One or more hosts can be designated for use only by HA-enabled VMs that are restarting due
    to a host failure. Setting up a pool of such dedicated HA hosts as the recovery destination for
    all HA-enabled VMs is useful to:</para>
  <itemizedlist>
    <listitem>
      <para>Make it easier to determine which VMs have been restarted as part of the CloudPlatform
        high-availability function. If a VM is running on a dedicated HA host, then it must be an
        HA-enabled VM whose original host failed. (With one exception: It is possible for an
        administrator to manually migrate any VM to a dedicated HA host.).</para>
    </listitem>
    <listitem>
      <para>Keep HA-enabled VMs from restarting on hosts which may be reserved for other
        purposes.</para>
    </listitem>
  </itemizedlist>
  <para>The dedicated HA option is set through a special host tag when the host is created. To allow
    the administrator to dedicate hosts to only HA-enabled VMs, set the global configuration
    variable ha.tag to the desired tag (for example, "ha_host"), and restart the Management Server.
    Enter the value in the Host Tags field when adding the host(s) that you want to dedicate to
    HA-enabled VMs.</para>
  <note>
    <para>If you set ha.tag, be sure to actually use that tag on at least one host in your cloud. If
      the tag specified in ha.tag is not set for any host in the cloud, the HA-enabled VMs will fail
      to restart after a crash.</para>
  </note>
  <para/>
</section>