openstack-manuals/doc/common/section_getstart_image.xml

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  xml:id="image-service-overview">
      <title>OpenStack Image Service</title>
      <para>The OpenStack Image Service is central to Infrastructure-as-a-Service (IaaS)
        as shown in <xref linkend="conceptual-architecture"/>. It accepts API requests
        for disk or server images, and image metadata from end users or OpenStack Compute
        components. It also supports the storage of disk or server images on various
        repository types, including OpenStack Object Storage.
        </para>
      <para>A number of periodic processes run on the OpenStack Image Service to
        support caching. Replication services ensure consistency and
        availability through the cluster. Other periodic processes
        include auditors, updaters, and reapers.</para>
      <para>The OpenStack Image Service includes the following
        components:</para>
      <variablelist>
        <varlistentry>
          <term><systemitem class="service">glance-api</systemitem></term>
          <listitem><para>Accepts Image API calls for image discovery,
           retrieval, and storage.</para></listitem>
        </varlistentry>
        <varlistentry>
          <term><systemitem class="service">glance-registry</systemitem></term>
          <listitem><para>Stores, processes, and retrieves metadata about
           images. Metadata includes items such as size and type.</para>
          <note><title>Security note</title>
          <para>The registry is a private internal service meant for use
           by OpenStack Image Service. Do not disclose it to
           users.</para></note>
        </listitem>
        </varlistentry>
        <varlistentry>
          <term>Database</term>
          <listitem><para>Stores image metadata and you can choose your database
           depending on your preference. Most deployments use MySQL or
           SQLite.</para></listitem>
        </varlistentry>
        <varlistentry>
          <term>Storage repository for image files</term>
          <listitem><para>Various repository types are supported including
           normal file systems, Object Storage, RADOS block devices, HTTP, and
           Amazon S3. Note that some repositories will only support
           read-only usage.</para></listitem>
       </varlistentry>
      </variablelist>
    </section>