Explain how to configure hypervisors to allow resize operations.

fix bug 1073619.

Change-Id: I2cf6cc202cccd0e96ef39d8035dc407547c4d57e

doc/src/docbkx/openstack-compute-admin/computeconfigure.xml

@@ -1114,8 +1114,45 @@ $ nova aggregate-set-metadata &lt;aggregate-id&gt; operational_state=created</pr
       </para>
     </section> <!-- End of Block migration -->
 
-    </section> <!-- End of XenServer -->
+    </section> <!-- End of XenServer/Migration -->
   </section> <!-- End of configuring migrations -->
+  <section xml:id="configuring-resize">
+    <?dbhtml stop-chunking?>
+    <title>Configuring Resize</title>
+    <para>Resize (or Server resize) is the ability to change the
+    flavor of a server, thus allowing it to upscale or downscale
+    according to user needs. In order for this feature
+    to work properly, some underlying virt layers may need further
+    configuration; this section describes the required configuration
+    steps for each hypervisor layer provided by OpenStack.</para>
+    <section xml:id="xenserver-resize">
+      <title>XenServer</title>
+      <para>To get resize to work with XenServer (and XCP) you need to:</para>
+      <itemizedlist>
+         <listitem><para>Establish a root trust between all hypervisor
+         nodes of your deployment:</para>
+         <para>You can simply do so, by generating an ssh key-pair (with ssh-keygen)
+         and then ensuring that each of your dom0's authorized_keys file
+         (located in /root/.ssh/authorized_keys) contains the public key fingerprint
+         (located in /root/.ssh/id_rsa.pub).</para>
+         </listitem>
+         <listitem><para>Provide a /images mountpoint to your hypervisor's dom0:</para>
+         <para>Dom0 space is a premium so creating a directory in dom0 is kind of
+         dangerous, and almost surely bound to fail especially when resizing big servers.
+         The least you can do is to symlink /images to your local storage SR. The
+         instructions below work for an English based installation of XenServer (and XCP)
+         and in the case of ext3 based SR (with which the resize functionality is
+         known to work correctly).</para>
+         <programlisting>
+sr_uuid=$(xe sr-list name-label="Local storage" params=uuid --minimal)
+img_dir="/var/run/sr-mount/$sr_uuid/images"
+mkdir -p "$img_dir"
+ln -s  $img_dir /images
+         </programlisting>
+         </listitem>
+      </itemizedlist>
+    </section> <!-- End of XenServer/Resize -->
+  </section> <!-- End of configuring resize -->
   <section xml:id="installing-moosefs-as-backend">
     <title>Installing MooseFS as shared storage for the instances directory</title>
     <para> In the previous section we presented a convenient way to deploy a shared storage using