openstack-manuals/doc/arch-design/compute_focus/section_prescriptive_examples_compute_focus.xml

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  xml:id="prescriptive-example-compute-focus">
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    <title>Prescriptive examples</title>
    <para>The Conseil Européen pour la Recherche Nucléaire (CERN),
        also known as the European Organization for, Nuclear Research
        provides particle accelerators and other infrastructure for
        high-energy physics research.</para>
    <para>As of 2011 CERN operated these two compute centers in Europe
        with plans to add a third.</para>
    <informaltable rules="all">
        <col width="40%" />
        <col width="60%" />
        <thead>
            <tr><th>Data center</th><th>Approximate capacity</th></tr>
            </thead>
        <tbody>
            <tr>
                <td>Geneva, Switzerland</td>
                <td>
                    <itemizedlist>
                        <listitem><para>3.5 Mega Watts</para></listitem>
                        <listitem><para>91000 cores</para></listitem>
                        <listitem><para>120 PB HDD</para></listitem>
                        <listitem><para>100 PB Tape</para></listitem>
                        <listitem><para>310 TB Memory</para></listitem>
                    </itemizedlist>
                </td>
            </tr>
            <tr>
                <td>Budapest, Hungary</td>
                <td>
                    <itemizedlist>
                        <listitem><para>2.5 Mega Watts</para></listitem>
                        <listitem><para>20000 cores</para></listitem>
                        <listitem><para>6 PB HDD</para></listitem>
                    </itemizedlist>
                </td>
            </tr>
        </tbody>
    </informaltable>
    <para>To support a growing number of compute heavy users of
        experiments related to the Large Hadron Collider (LHC) CERN
        ultimately elected to deploy an OpenStack cloud using
        Scientific Linux and RDO. This effort aimed to simplify the
        management of the center's compute resources with a view to
        doubling compute capacity through the addition of an
        additional data center in 2013 while maintaining the same
        levels of compute staff.</para>
    <para>The CERN solution uses <glossterm baseform="cell">cells</glossterm>
        for segregation of compute
        resources and to transparently scale between different data
        centers. This decision meant trading off support for security
        groups and live migration. In addition some details like
        flavors needed to be manually replicated across cells. In
        spite of these drawbacks cells were determined to provide the
        required scale while exposing a single public API endpoint to
        users.</para>
    <para>A compute cell was created for each of the two original data
        centers and a third was created when a new data center was
        added in 2013. Each cell contains three availability zones to
        further segregate compute resources and at least three
        RabbitMQ message brokers configured to be clustered with
        mirrored queues for high availability.</para>
    <para>The API cell, which resides behind a HAProxy load balancer,
        is located in the data center in Switzerland and directs API
        calls to compute cells using a customized variation of the
        cell scheduler. The customizations allow certain workloads to
        be directed to a specific data center or "all" data centers
        with cell selection determined by cell RAM availability in the
        latter case.</para>
    <mediaobject>
        <imageobject>
            <imagedata contentwidth="4in" fileref="../figures/Generic_CERN_Example.png"/>
        </imageobject>
    </mediaobject>
    <para>There is also some customization of the filter scheduler
        that handles placement within the cells:</para>
    <itemizedlist>
        <listitem><para>ImagePropertiesFilter - To provide special handling
                depending on the guest operating system in use
                (Linux-based or Windows-based).</para>
        </listitem>
        <listitem><para>ProjectsToAggregateFilter - To provide special
                handling depending on the project the instance is
                associated with.</para>
        </listitem>
        <listitem><para>default_schedule_zones - Allows the selection of
                multiple default availability zones, rather than a
                single default.
        </para></listitem>
    </itemizedlist>
    <para>The MySQL database server in each cell is managed by a
        central database team and configured in an active/passive
        configuration with a NetApp storage back end. Backups are
        performed ever 6 hours.</para>
    <section xml:id="network-architecture">
      <title>Network architecture</title>
    <para>To integrate with existing CERN networking infrastructure
        customizations were made to legacy networking (nova-network). This was in the
        form of a driver to integrate with CERN's existing database
        for tracking MAC and IP address assignments.</para>
    <para>The driver facilitates selection of a MAC address and IP for
        new instances based on the compute node the scheduler places
        the instance on</para>
    <para>The driver considers the compute node that the scheduler
        placed an instance on and then selects a MAC address and IP
        from the pre-registered list associated with that node in the
        database. The database is then updated to reflect the instance
        the addresses were assigned to.</para></section>
    <section xml:id="storage-architecture">
      <title>Storage architecture</title>
    <para>The OpenStack Image Service is deployed in the API cell and
        configured to expose version 1 (V1) of the API. As a result
        the image registry is also required. The storage back end in
        use is a 3 PB Ceph cluster.</para>
    <para>A small set of "golden" Scientific Linux 5 and 6 images are
        maintained which applications can in turn be placed on using
        orchestration tools. Puppet is used for instance configuration
        management and customization but Orchestration deployment is
        expected.</para></section>
    <section xml:id="monitoring">
      <title>Monitoring</title>
    <para>Although direct billing is not required, the Telemetry module
        is used to perform metering for the purposes of adjusting
        project quotas. A sharded, replicated, MongoDB back end is
        used. To spread API load, instances of the nova-api service
        were deployed within the child cells for Telemetry to query
        against. This also meant that some supporting services
        including keystone, glance-api and glance-registry needed to
        also be configured in the child cells.</para>
    <mediaobject>
        <imageobject>
            <imagedata contentwidth="4in"
                fileref="../figures/Generic_CERN_Architecture.png"/>
        </imageobject>
    </mediaobject>
    <para>
        Additional monitoring tools in use include <link
        xlink:href="http://flume.apache.org/">Flume</link>, <link
        xlink:href="http://www.elasticsearch.org/">Elastic
        Search</link>, <link
        xlink:href="http://www.elasticsearch.org/overview/kibana/">Kibana</link>,
        and the CERN developed <link
        xlink:href="http://lemon.web.cern.ch/lemon/index.shtml">Lemon</link>
        project.
    </para>
    </section>
    <section xml:id="references-cern-resources"><title>References</title>
    <para>The authors of the Architecture Design Guide would like to
        thank CERN for publicly documenting their OpenStack deployment
        in these resources, which formed the basis for this
        chapter:</para>
    <itemizedlist>
        <listitem><para><link xlink:href="http://openstack-in-production.blogspot.fr">http://openstack-in-production.blogspot.fr</link>
        </para></listitem>
        <listitem><para>
              <link
              xlink:href="http://www.openstack.org/assets/presentation-media/Deep-Dive-into-the-CERN-Cloud-Infrastructure.pdf">Deep
              dive into the CERN Cloud Infrastructure</link></para>
        </listitem>
    </itemizedlist></section>
</section>