docs/en-US/changing-service-offering-for-vm.xml

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<section id="changing-service-offering-for-vm">
  <title>Changing the Service Offering for a VM</title>
  <para>To upgrade or downgrade the level of compute resources available to a virtual machine, you
    can change the VM's compute offering.</para>
  <orderedlist>
    <listitem>
      <para>Log in to the &PRODUCT; UI as a user or admin.</para>
    </listitem>
    <listitem>
      <para>In the left navigation, click Instances.</para>
    </listitem>
    <listitem>
      <para>Choose the VM that you want to work with.</para>
    </listitem>
    <listitem>
      <para>(Skip this step if you have enabled dynamic VM scaling; see <xref
          linkend="change-cpu-ram-for-vm"/>.)</para>
      <para>Click the Stop button to stop the VM. <inlinemediaobject>
          <imageobject>
            <imagedata fileref="./images/stop-instance-icon.png"/>
          </imageobject>
          <textobject>
            <phrase>StopButton.png: button to stop a VM</phrase>
          </textobject>
        </inlinemediaobject>
      </para>
    </listitem>
    <listitem>
      <para>Click the Change Service button.<inlinemediaobject>
          <imageobject>
            <imagedata fileref="./images/change-service-icon.png"/>
          </imageobject>
          <textobject>
            <phrase>ChangeServiceButton.png: button to change the service of a VM</phrase>
          </textobject>
        </inlinemediaobject></para>
      <para>The Change service dialog box is displayed.</para>
    </listitem>
    <listitem>
      <para>Select the offering you want to apply to the selected VM.</para>
    </listitem>
    <listitem>
      <para>Click OK.</para>
    </listitem>
  </orderedlist>
  <section id="change-cpu-ram-for-vm">
    <!-- CS-17394 -->
    <title>CPU and Memory Scaling for Running VMs</title>
    <para>(Supported on VMware and XenServer)</para>
    <para>It is not always possible to accurately predict the CPU and RAM requirements when you
      first deploy a VM. You might need to increase these resources at any time during the life of a
      VM. You can dynamically modify CPU and RAM levels to scale up these resources for a running VM
      without incurring any downtime.</para>
    <para>Dynamic CPU and RAM scaling can be used in the following cases:</para>
    <itemizedlist>
      <listitem>
        <para>User VMs on hosts running VMware and XenServer.</para>
      </listitem>
      <listitem>
        <para>System VMs on VMware.</para>
      </listitem>
      <listitem>
        <para>VMware Tools or XenServer Tools must be installed on the virtual machine.</para>
      </listitem>
      <listitem>
        <para>The new requested CPU and RAM values must be within the constraints allowed by the
          hypervisor and the VM operating system.</para>
      </listitem>
      <listitem>
        <para>New VMs that are created after the installation of &PRODUCT; 4.2 can use the dynamic
          scaling feature. If you are upgrading from a previous version of &PRODUCT;, your existing
          VMs created with previous versions will not have the dynamic scaling capability unless you
          update them using the following procedure.</para>
      </listitem>
    </itemizedlist>
  </section>
  <section id="update-vms">
    <title>Updating Existing VMs</title>
    <para>If you are upgrading from a previous version of &PRODUCT;, and you want your existing VMs
      created with previous versions to have the dynamic scaling capability, update the VMs using
      the following steps:</para>
    <orderedlist>
      <listitem>
        <para>Make sure the zone-level setting enable.dynamic.scale.vm is set to true. In the left
          navigation bar of the &PRODUCT; UI, click Infrastructure, then click Zones, click the zone
          you want, and click the Settings tab.</para>
      </listitem>
      <listitem>
        <para>Install Xen tools (for XenServer hosts) or VMware Tools (for VMware hosts) on each VM
          if they are not already installed.</para>
      </listitem>
      <listitem>
        <para>Stop the VM.</para>
      </listitem>
      <listitem>
        <para>Click the Edit button.</para>
      </listitem>
      <listitem>
        <para>Click the Dynamically Scalable checkbox.</para>
      </listitem>
      <listitem>
        <para>Click Apply.</para>
      </listitem>
      <listitem>
        <para>Restart the VM.</para>
      </listitem>
    </orderedlist>
  </section>
  <section id="configure-dynamic-scaling">
    <title>Configuring Dynamic CPU and RAM Scaling</title>
    <para>To configure this feature, use the following new global configuration variables:</para>
    <itemizedlist>
      <listitem>
        <para>enable.dynamic.scale.vm: Set to True to enable the feature. By default, the feature is
          turned off.</para>
      </listitem>
      <listitem>
        <para>scale.retry: How many times to attempt the scaling operation. Default = 2.</para>
      </listitem>
    </itemizedlist>
  </section>
  <section id="dynamic-scaling-howto">
    <title>How to Dynamically Scale CPU and RAM</title>
    <para>To modify the CPU and/or RAM capacity of a virtual machine, you need to change the compute
      offering of the VM to a new compute offering that has the desired CPU and RAM values. You can
      use the same steps described above in <xref linkend="changing-service-offering-for-vm"/>, but
      skip the step where you stop the virtual machine. Of course, you might have to create a new
      compute offering first.</para>
    <para>When you submit a dynamic scaling request, the resources will be scaled up on the current
      host if possible. If the host does not have enough resources, the VM will be live migrated to
      another host in the same cluster. If there is no host in the cluster that can fulfill the
      requested level of CPU and RAM, the scaling operation will fail. The VM will continue to run
      as it was before.</para>
  </section>
  <section id="dynamic-scaling-limitations">
    <title>Limitations</title>
    <itemizedlist>
      <listitem>
        <para>You can not do dynamic scaling for system VMs on XenServer.</para>
      </listitem>
      <listitem>
        <para>&PRODUCT; will not check to be sure that the new CPU and RAM levels are compatible
          with the OS running on the VM.</para>
      </listitem>
      <listitem>
        <para>When scaling memory or CPU for a Linux VM on VMware, you might need to run scripts in
          addition to the other steps mentioned above. For more information, see <ulink
            url="http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&amp;cmd=displayKC&amp;externalId=1012764"
            >Hot adding memory in Linux (1012764)</ulink> in the VMware Knowledge Base.</para>
      </listitem>
      <listitem>
        <para>(VMware) If resources are not available on the current host, scaling up will fail on
          VMware because of a known issue where &PRODUCT; and vCenter calculate the available
          capacity differently. For more information, see <ulink
            url="https://issues.apache.org/jira/browse/CLOUDSTACK-1809"
            >https://issues.apache.org/jira/browse/CLOUDSTACK-1809</ulink>.</para>
      </listitem>
      <listitem>
        <para>On VMs running Linux 64-bit and Windows 7 32-bit operating systems, if the VM is
          initially assigned a RAM of less than 3 GB, it can be dynamically scaled up to 3 GB, but
          not more. This is due to a known issue with these operating systems, which will freeze if
          an attempt is made to dynamically scale from less than 3 GB to more than 3 GB. </para>
      </listitem>
    </itemizedlist>
  </section>
</section>