openstack-manuals/doc/arch-design/generalpurpose/section_user_requirements_general_purpose.xml

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  xml:id="user-requirements-general-purpose">
    <?dbhtml stop-chunking?>
    <title>User requirements</title>
    <para>When building a general purpose cloud, you should follow the
        <glossterm baseform="IaaS">Infrastructure-as-a-Service (IaaS)</glossterm>
        model; a platform best suited for use cases with simple requirements.
        General purpose cloud user requirements are not complex.
        However, it is important to capture them even
        if the project has minimum business and technical requirements, such as a
        proof of concept (PoC), or a small lab platform.</para>
      <note>
        <para>
          The following user considerations are written from the perspective of
          the cloud builder, not from the perspective of the end user.
        </para>
      </note>
    <variablelist>
      <varlistentry>
        <term>Cost</term>
        <listitem>
            <para>Financial factors are a primary concern for
                any organization. Cost is an important criterion
                as general purpose clouds are considered the baseline
                from which all other cloud architecture environments
                derive. General purpose clouds do not always provide
                the most cost-effective environment for specialized
                applications or situations. Unless razor-thin margins and costs have
                been mandated as a critical factor, cost should not be
                the sole consideration when choosing or designing a
                general purpose architecture.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>Time to market</term>
        <listitem>
            <para>The ability to deliver services or products within
                a flexible time frame is a common business factor
                when building a general purpose cloud. In today's high-speed business world,
                the ability to deliver a product in six months instead
                of two years is a driving force behind the
                decision to build general purpose clouds. General
                purpose clouds allow users to self-provision and gain
                access to compute, network, and storage resources
                on-demand thus decreasing time to market.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>Revenue opportunity</term>
        <listitem>
            <para>Revenue opportunities for a
                cloud will vary greatly based on the intended
                use case of that particular cloud. Some general
                purpose clouds are built for commercial customer
                facing products, but there are alternatives
                that might make the general purpose cloud the right
                choice. For example, a small cloud service provider (CSP) might
                want to build a general purpose cloud rather than a
                massively scalable cloud because they do not have the
                deep financial resources needed, or because they do
                not, or will not, know in advance the purposes for which
                their customers are going to use the cloud. For some
                users, the advantages cloud itself offers mean an
                enhancement of revenue opportunity. For others, the
                fact that a general purpose cloud provides only
                baseline functionality will be a disincentive for use,
                leading to a potential stagnation of potential revenue
                opportunities.</para>
        </listitem>
      </varlistentry>
    </variablelist>
    <section xml:id="technical-requirements">
      <title>Technical requirements</title>
    <para>Technical cloud architecture requirements should be weighted
        against the business requirements.
    </para>
    <variablelist>
      <varlistentry>
        <term>Performance</term>
        <listitem>
            <para>As a baseline product, general purpose
                clouds do not provide optimized performance for any
                particular function. While a general purpose cloud
                should provide enough performance to satisfy average
                user considerations, performance is not a general
                purpose cloud customer driver.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>No predefined usage model</term>
        <listitem>
            <para>The lack of a pre-defined
                usage model enables the user to run a wide variety of
                applications without having to know the application
                requirements in advance. This provides a degree of
                independence and flexibility that no other cloud
                scenarios are able to provide.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>On-demand and self-service application</term>
        <listitem>
            <para>By
                definition, a cloud provides end users with the
                ability to self-provision computing power, storage,
                networks, and software in a simple and flexible way.
                The user must be able to scale their resources up to a
                substantial level without disrupting the underlying
                host operations. One of the benefits of using a
                general purpose cloud architecture is the ability to
                start with limited resources and increase them over
                time as the user demand grows.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>Public cloud</term>
        <listitem>
            <para>For a company interested in building a
                commercial public cloud offering based on OpenStack,
                the general purpose architecture model might be the
                best choice. Designers are not always going to
                know the purposes or workloads for which the end users
                will use the cloud.</para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>Internal consumption (private) cloud</term>
        <listitem>
            <para>Organizations need to determine if it is logical to
                create their own clouds internally. Using a private cloud,
                organizations are able to maintain complete control over
                architectural and cloud components.</para>
              <note>
                <para>Users will want to combine
                using the internal cloud with access to an external
                cloud. If that case is likely, it might be worth
                exploring the possibility of taking a multi-cloud
                approach with regard to at least some of the
                architectural elements.
                </para>
              </note>
            <para>Designs that incorporate the
                use of multiple clouds, such as a private cloud and a
                public cloud offering, are described in the
                "Multi-Cloud" scenario, see <xref linkend="multi_site"/>.
            </para>
        </listitem>
      </varlistentry>
      <varlistentry>
        <term>Security</term>
        <listitem>
            <para>Security should be implemented according
                to asset, threat, and vulnerability risk assessment
                matrices. For cloud domains that require increased
                computer security, network security, or information
                security, a general purpose cloud is not considered an
                appropriate choice.</para>
        </listitem>
      </varlistentry>
    </variablelist>
  </section>
</section>