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CLOUDSTACK-867. DOC. Document dynamic CPU and RAM scaling for running VMs.

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docs/en-US/changing-service-offering-for-vm.xml
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@ -28,7 +28,8 @@
<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>Click the Stop button to stop the VM.<inlinemediaobject>
<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>
@ -50,5 +51,49 @@
<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">
<!-- CLOUDSTACK-658 -->
<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 or decrease these resources at any time during the life of a VM.
You can dynamically modify CPU and RAM levels to
change 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>New VMs that are created
after the installation of &PRODUCT; 4.2.
If you are upgrading from a previous version of &PRODUCT;,
your existing VMs created with previous versions
will not have the dynamic scaling capability.</para>
</listitem>
<listitem><para>User VMs on hosts running VMware and XenServer.</para></listitem>
<listitem><para>System VMs on VMware.</para></listitem>
<listitem><para>VM 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>
</itemizedlist>
<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>
<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>
<warning><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></warning>
</section>
</section>