openstack-manuals/doc/arch-design/massively_scalable/section_user_requirements_massively_scalable.xml

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  xml:id="user-requirements-massive-scale-overview">
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    <title>User requirements</title>
    <para>Defining user requirements for a massively scalable OpenStack
        design architecture dictates approaching the design from two
        different, yet sometimes opposing, perspectives: the cloud
        user, and the cloud operator. The expectations and perceptions
        of the consumption and management of resources of a massively
        scalable OpenStack cloud from these two perspectives are
        distinctly different.</para>
    <para>Massively scalable OpenStack clouds have the following user
        requirements:</para>
    <itemizedlist>
        <listitem>
            <para>The cloud user expects repeatable, dependable, and
                deterministic processes for launching and deploying
                cloud resources. You could deliver this through a
                web-based interface or publicly available API
                endpoints. All appropriate options for requesting
                cloud resources must be available through some type
                of user interface, a command-line interface (CLI), or
                API endpoints.</para>
        </listitem>
        <listitem>
            <para>Cloud users expect a fully self-service and
                on-demand consumption model. When an OpenStack cloud
                reaches the "massively scalable" size, expect
                consumption "as a service" in each and
                every way.</para>
        </listitem>
        <listitem>
            <para>For a user of a massively scalable OpenStack public
                cloud, there are no expectations for control over
                security, performance, or availability. Users expect
                only SLAs related to uptime of API services, and
                very basic SLAs for services offered. It is the user's
                responsibility to address these issues on their own.
                The exception to this expectation is the rare case of
                a massively scalable cloud infrastructure built for
                a private or government organization that has
                specific requirements.</para>
        </listitem>
    </itemizedlist>
    <para>The cloud user's requirements and expectations that determine
        the cloud design focus on the consumption model. The user
        expects to consume cloud resources in an automated and
        deterministic way, without any need for knowledge of the
        capacity, scalability, or other attributes of the cloud's
        underlying infrastructure.</para>
    <section xml:id="operator-requirements-massive-scale">
      <title>Operator requirements</title>
    <para>While the cloud user can be completely unaware of the
        underlying infrastructure of the cloud and its attributes, the
        operator must build and support the infrastructure for operating
        at scale. This presents a very demanding set of requirements
        for building such a cloud from the operator's perspective:</para>
    <itemizedlist>
        <listitem>
            <para>Everything must be capable of automation. For example,
                everything from compute hardware, storage hardware,
                networking hardware, to the installation and
                configuration of the supporting software. Manual
                processes are impractical in a massively scalable
                OpenStack design architecture.</para>
        </listitem>
        <listitem>
            <para>The cloud operator requires that capital expenditure
                (CapEx) is minimized at all layers of the stack.
                Operators of massively scalable OpenStack clouds
                require the use of dependable commodity hardware and
                freely available open source software components to
                reduce deployment costs and operational expenses.
                Initiatives like OpenCompute (more information
                available at <link
                xlink:href="http://www.opencompute.org">http://www.opencompute.org</link>)
                provide additional information and pointers. To cut
                costs, many operators sacrifice redundancy. For
                example, using redundant power supplies, network
                connections, and rack switches.</para>
        </listitem>
        <listitem>
            <para>Companies operating a massively scalable OpenStack
                cloud also require that operational expenditures
                (OpEx) be minimized as much as possible. We
                recommend using cloud-optimized hardware when
                managing operational overhead. Some of
                the factors to consider include power,
                cooling, and the physical design of the chassis. Through
                customization, it is possible to optimize the hardware
                and systems for this type of workload because of the
                scale of these implementations.</para>
        </listitem>
        <listitem>
            <para>Massively scalable OpenStack clouds require
                extensive metering and monitoring functionality to
                maximize the operational efficiency by keeping the
                operator informed about the status and state of the
                infrastructure. This includes full scale metering of
                the hardware and software status. A corresponding
                framework of logging and alerting is also required to
                store and enable operations to act on the meters
                provided by the metering and monitoring solutions.
                The cloud operator also needs a solution that uses the
                data provided by the metering and monitoring solution
                to provide capacity planning and capacity trending
                analysis.</para>
        </listitem>
        <listitem>
            <para>Invariably, massively scalable OpenStack clouds extend
                over several sites. Therefore, the user-operator
                requirements for a multi-site OpenStack architecture
                design are also applicable here. This includes various
                legal requirements; other jurisdictional legal or
                compliance requirements; image
                consistency-availability; storage replication and
                availability (both block and file/object storage); and
                authentication, authorization, and auditing (AAA).
                See <xref linkend="multi_site"/>
                for more details on requirements and considerations
                for multi-site OpenStack clouds.</para>
        </listitem>
        <listitem>
            <para>The design architecture of a massively scalable OpenStack
                cloud must address considerations around physical
                facilities such as space, floor weight, rack height and
                type, environmental considerations, power usage and power
                usage efficiency (PUE), and physical security.</para>
        </listitem>
    </itemizedlist></section>
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