openstack-manuals/doc/config-reference/compute/section_hypervisor_xen_libvirt.xml

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  xml:id="xen_libvirt">
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    <title>Xen via Libvirt</title>
    <para>OpenStack Compute supports the Xen Project Hypervisor (or Xen). Xen can be integrated with
        OpenStack Compute via the <link xlink:href="http://libvirt.org/">libvirt</link>
        <link xlink:href="http://wiki.xen.org/wiki/Choice_of_Toolstacks">toolstack</link> or via the
            <link xlink:href="http://xenproject.org/developers/teams/xapi.html">XAPI</link>
        <link xlink:href="http://wiki.xen.org/wiki/Choice_of_Toolstacks">toolstack</link>. This
        section describes how to set up OpenStack Compute with Xen and libvirt. For information on
        how to set up Xen with XAPI refer to <xref linkend="section_hypervisor_xen_xapi"/>.</para>
    <section xml:id="xen-libvirt-install">
        <title>Installing Xen with Libvirt</title>
        <para>At this stage we recommend to use the baseline that we use for the <link
                xlink:href="http://wiki.xenproject.org/wiki/OpenStack_CI_Loop_for_Xen-Libvirt">Xen
                Project OpenStack CI Loop</link>, which contains the most recent stability fixes to
            both Xen and Libvirt.</para>
        <para><link
                xlink:href="http://www.xenproject.org/downloads/xen-archives/xen-45-series/xen-451.html"
            >Xen 4.5.1</link> (or newer) and <link xlink:href="http://libvirt.org/sources/"
                >Libvirt 1.2.15</link> (or newer) contain the most recent OpenStack improvements for
            Xen. The necessary Xen changes have also been backported to the Xen 4.4.3 stable branch
            (not yet released at this stage). Please check with the Linux and FreeBSD distros you
            are intending to use as <link
                xlink:href="http://wiki.xenproject.org/wiki/Category:Host_Install">Dom 0</link>,
            whether the relevant version of Xen and Libvirt are available as installable
            packages.</para>
        <para>The latest releases of Xen and libvirt packages that fulfil the above minimum
            requirements for the various openSUSE distributions can always be found and installed
            from the <link xlink:href="https://build.opensuse.org/project/show/Virtualization">Open
                Build Service</link> Virtualization project. To install these latest packages, add
            the Virtualization repository to your software management stack and get the newest
            packages from there. More information about the latest Xen and Libvirt packages are
            available <link xlink:href="https://build.opensuse.org/package/show/Virtualization/xen"
                >here</link> and <link
                xlink:href="https://build.opensuse.org/package/show/Virtualization/libvirt"
                >here</link>.</para>
        <para>Alternatively, it is possible to use the Ubuntu LTS 14.04 Xen Package
                <emphasis>4.4.1-0ubuntu0.14.04.4</emphasis> (Xen 4.4.1) and apply the patches
            outlined <link
                xlink:href="http://wiki.xenproject.org/wiki/OpenStack_CI_Loop_for_Xen-Libvirt#Baseline"
                >here</link>. You can also use the Ubuntu LTS 14.04 libvirt package <emphasis>1.2.2
                libvirt_1.2.2-0ubuntu13.1.7</emphasis> as baseline and update it to libvirt version
            1.2.15, or 1.2.14 with the patches outlined <link
                xlink:href="http://wiki.xenproject.org/wiki/OpenStack_CI_Loop_for_Xen-Libvirt#Baseline"
                >here</link> applied. Note that this will require re-build these packages partly
            from source.</para>
        <para>For further information and latest developments, you may want to consult the Xen
            Project's <link
                xlink:href="http://lists.xenproject.org/cgi-bin/mailman/listinfo/wg-openstack"
                >mailing lists for OpenStack related issues and questions</link>.</para>
    </section>
    <section xml:id="xen-libvirt-configuration">
        <title>Configuring Xen with Libvirt</title>
        <para>To enable Xen via libvirt, ensure the following options are set in
        <filename>/etc/nova/nova.conf</filename> on all hosts running the <systemitem class="service"
            >nova-compute</systemitem>
        service.<programlisting language="ini">compute_driver = libvirt.LibvirtDriver

[libvirt]
virt_type = xen</programlisting></para>
    </section>
    <section xml:id="xen-libvirt-additional-configuration">
        <title>Additional configuration options</title>
        <para>Use the following as a guideline for configuring Xen for use in OpenStack:</para>
        <orderedlist>
            <listitem>
                <para><emphasis role="bold">Dom0 Memory:</emphasis> Set it between 1GB and 4GB by
                    adding the following parameter to the Xen Boot Options in the <filename><link
                        xlink:href="http://xenbits.xen.org/docs/unstable/misc/xen-command-line.html"
                        >grub.conf</link></filename> file.
                    <programlisting language="ini">dom0_mem=1024M</programlisting></para>
                <note><para>Note that the above memory limits are suggestions and should be based on
                the available compute host resources. For large hosts, that will run many hundred of
                instances,the chosen values may need to be higher.</para></note>
                <note><para>The location of the grub.conf file depends on the host Linux
                    distribution that you are using. Please refer to the distro documentation for
                    more details (see <link xlink:href="http://wiki.xenproject.org/wiki/Category:Host_Install"
                    >Dom 0</link> for more resources).</para></note>
            </listitem>
            <listitem>
                <para><emphasis role="bold">Dom0 vcpus:</emphasis> Set the virtual CPUs to 4 and
                    employ CPU pinning by adding the following parameters to the Xen Boot Options in the
                    <filename><link
                        xlink:href="http://xenbits.xen.org/docs/unstable/misc/xen-command-line.html"
                        >grub.conf</link></filename> file.
                    <programlisting language="ini">dom0_max_vcpus=4 dom0_vcpus_pin</programlisting></para>
                <note><para>Note that the above virtual CPU limits are suggestions and should be based on
                    the available compute host resources. For large hosts, that will run many hundred of
                    instances, the suggested values may need to be higher.</para></note>
            </listitem>
            <listitem>
                <para><emphasis role="bold">PV vs HVM guests:</emphasis> A Xen virtual machine can
                    be paravirtualized (PV) or hardware virtualized (HVM). The virtualization mode
                    determines the interaction between Xen, Dom 0, and the guest VM's kernel. PV guests
                    are aware of the fact that they are virtualized and will co-operate with Xen and
                    Dom 0. The choice of virtualization mode determines performance characteristics.
                    For an overview of Xen virtualization modes, see
                    <link xlink:href="http://wiki.xen.org/wiki/Xen_Overview#Guest_Types">
                        Xen Guest Types</link>.</para>
                <para>In OpenStack, customer VMs may run in either PV or HVM mode. The mode is a
                    property of the operating system image used by the VM, and is changed by
                    adjusting the image metadata stored in the glance image service. The image
                    metadata can be changed using the nova or glance commands.
                </para>
                <para>
                    To choose one of the HVM modes (HVM, HVM with PV Drivers or PVHVM) use nova or
                    glance to set the vm_mode property to hvm</para>
                <para>To choose one of the HVM modes (HVM, HVM with PV Drivers or PVHVM) use one of
                    the following two commands
                    <screen><prompt>$</prompt> <userinput>nova image-meta <replaceable>img-uuid</replaceable> set vm_mode=hvm</userinput></screen>
                    <screen><prompt>$</prompt> <userinput>glance image-update <replaceable>img-uuid</replaceable> --property vm_mode=hvm</userinput></screen>
                    To chose PV mode, which is supported by NetBSD, FreeBSD and Linux, useone of
                    the following two commands
                    <screen><prompt>$</prompt> <userinput>nova image-meta <replaceable>img-uuid</replaceable> set vm_mode=xen</userinput></screen>
                    <screen><prompt>$</prompt> <userinput>glance image-update <replaceable>img-uuid</replaceable> --property vm_mode=xen</userinput></screen>
                </para>
                <note><para>The default for virtualization mode in nova is PV mode.</para></note>
            </listitem>
            <listitem>
                 <para><emphasis role="bold">Image Formats:</emphasis> Xen supports raw, qcow2 and vhd
                     image formats. For more information on image formats, refer to the <link
                         xlink:href="http://docs.openstack.org/image-guide/introduction.html"
                         >OpenStack Virtual Image Guide</link> and the <link
                             xlink:href="http://wiki.xenproject.org/wiki/Storage_options"
                             >Storage Options Guide on the Xen Project Wiki</link>.</para>
            </listitem>
            <listitem>
                <para><emphasis role="bold">Image Metadata:</emphasis> In addition to the vm_mode property
                    discussed above, the hypervisor_type property is another important component of the image
                    metadata, especially if your cloud contains mixed hypervisor compute nodes. Setting the
                    hypervisor_type property allows the nova scheduler to select a compute node
                    running the specified hypervisor when launching instances of the image. Image
                    metadata such as vm_mode, hypervisor_type, architecture, and others can be set
                    when importing the image to glance. The metatdata can also be changed using the
                    nova or glance commands:
                    <screen><prompt>$</prompt> <userinput>nova image-meta <replaceable>img-uuid</replaceable> set hypervisor_type=xen vm_mode=hvm</userinput></screen>
                    <screen><prompt>$</prompt> <userinput>glance image-update <replaceable>img-uuid</replaceable> --property hypervisor_type=xen --property vm_mode=hvm</userinput></screen>
                </para>
                <para>For more more information on image metadata, refer to the <link
                    xlink:href="http://docs.openstack.org/image-guide/image-metadata.html"
                    >OpenStack Virtual Image Guide</link>.
                </para>
            </listitem>
        </orderedlist>
        <para>To customize the libvirt driver, use the configuration option settings documented in
            <xref linkend="config_table_nova_xen"/>.
        </para>
    </section>
    <section xml:id="xen-libvirt-troubleshoot">
        <title>Troubleshoot Xen with Libvirt</title>
        <itemizedlist>
            <listitem>
                <para><emphasis role="bold">Important Log Files:</emphasis> When an instance fails to start, or when
                    you come across other issues, you should first consult the following log files:
                    <itemizedlist>
                        <listitem><para><filename>/var/log/nova/compute.log</filename> (for more information refer to
                            <xref linkend="section_nova-logs"/>).</para></listitem>
                        <listitem><para><filename>/var/log/libvirt/libxl/libxl-driver.log</filename>,</para></listitem>
                        <listitem><para><filename>/var/log/xen/qemu-dm-${instancename}.log</filename>,</para></listitem>
                        <listitem><para><filename>/var/log/xen/xen-hotplug.log</filename>,</para></listitem>
                        <listitem><para><filename>/var/log/xen/console/guest-${instancename}</filename> (to enable see <link
                            xlink:href="http://wiki.xen.org/wiki/Reporting_Bugs_against_Xen#Guest_console_logs"
                            >Enabling Guest Console Logs</link>) and</para>
                        </listitem>
                        <listitem><para>Host Console Logs (read <link
                            xlink:href="http://wiki.xen.org/wiki/Reporting_Bugs_against_Xen#Host_console_logs"
                            >Enabling and Retrieving Host Console Logs</link>).</para>
                        </listitem>
                    </itemizedlist>
                </para>
                <para>If you need further help you can ask questions on the mailing lists <link
                        xlink:href="http://lists.xenproject.org/cgi-bin/mailman/listinfo/xen-users"
                        >xen-users@</link>, <link
                        xlink:href="http://lists.xenproject.org/cgi-bin/mailman/listinfo/wg-openstack"
                        >wg-openstack@</link> or <link
                        xlink:href="http://wiki.xen.org/wiki/Reporting_Bugs_against_Xen">raise a
                        bug</link> against Xen.</para>
            </listitem>
        </itemizedlist>
    </section>
    <section xml:id="xen-libvirt-known-issues">
        <title>Known issues</title>
        <itemizedlist>
            <listitem>
                <para>Xen via libvirt is currently only supported with nova networking. A number of bugs
                are currently worked on to make sure that Xen via libvirt will also work with Neutron.</para>
            </listitem>
        </itemizedlist>
    </section>
    <section xml:id="xen-libvirt-additional-information">
        <title>Additional information and resources</title>
        <para>The following section contains links to other useful resources</para>
        <itemizedlist>
            <listitem>
                <para><link
                    xlink:href="http://wiki.xenproject.org/wiki/OpenStack"
                    >wiki.xenproject.org/wiki/OpenStack</link> - OpenStack Documentation on the Xen Project wiki</para>
            </listitem>
            <listitem>
                <para><link
                    xlink:href="http://wiki.xenproject.org/wiki/OpenStack_CI_Loop_for_Xen-Libvirt"
                    >wiki.xenproject.org/wiki/OpenStack_CI_Loop_for_Xen-Libvirt</link> - Information about the
                    Xen Project OpenStack CI Loop</para>
            </listitem>
            <listitem>
                <para><link
                    xlink:href="http://wiki.xenproject.org/wiki/OpenStack_via_DevStack"
                    >wiki.xenproject.org/wiki/OpenStack_via_DevStack</link> - How to set up OpenStack via DevStack</para>
            </listitem>
            <listitem>
                <para><link
                    xlink:href="http://lists.xenproject.org/cgi-bin/mailman/listinfo/wg-openstack"
                    >Mailing lists for OpenStack related issues and questions</link> - This list is dedicated
                to coordinating bug fixes and issues across Xen, libvirt and OpenStack and the CI loop.</para>
            </listitem>
        </itemizedlist>
    </section>
</section>