3981735acd
Edit wording; changed term/description lists to variable lists as per writing conventions backport: none Partial-Bug: #1251195 Change-Id: I3b7f3fedafa79ab64f75260fcd3c5daa7cbb5e34
196 lines
10 KiB
XML
196 lines
10 KiB
XML
<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0"
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xml:id="compute-service">
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<title>OpenStack Compute</title>
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<para>OpenStack Compute is used to host and manage cloud computing systems and
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is a major part of an infrastructure-as-a-service (IaaS) system. The main
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modules are implemented in Python.</para>
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<para>OpenStack Compute interacts with OpenStack Identity for
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authentication, OpenStack Image Service for images, and OpenStack dashboard
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for the user and administrative interface. Access to images is limited
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by project and by user; quotas are limited per project (for example, the
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number of instances). OpenStack Compute can scale horizontally on standard
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hardware, and download images to launch instances.</para>
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<para>OpenStack Compute consists of the following areas and their
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components:</para>
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<variablelist><title>API</title>
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<varlistentry>
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<term><systemitem class="service">nova-api service</systemitem></term>
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<listitem><para>Accepts and responds to end user compute API calls.
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Supports the OpenStack Compute API, the Amazon EC2 API, and a special
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Admin API for privileged users to perform administrative actions. It
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enforces some policies and initiates most orchestration activities,
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such as running an instance.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><systemitem class="service">nova-api-metadata</systemitem>
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service</term>
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<listitem><para>Accepts metadata requests from instances. The
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<systemitem class="service">nova-api-metadata</systemitem>
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service is generally used when you run in multi-host mode
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with <systemitem class="service">nova-network</systemitem>
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installations. For details, see <link
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xlink:href="http://docs.openstack.org/admin-guide-cloud/content/section_metadata-service.html"
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>Metadata service</link> in the <citetitle>Cloud
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Administrator Guide</citetitle>.</para>
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<para>On Debian systems, it is included in the <systemitem
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class="service">nova-api</systemitem> package, and can be
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selected through <package>debconf</package>.</para></listitem>
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</varlistentry>
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</variablelist>
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<variablelist>
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<title>Compute core</title>
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<varlistentry>
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<term><systemitem class="service">nova-compute</systemitem>
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process</term> <listitem><para>A worker daemon that creates and
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terminates virtual machine instances through hypervisor APIs. For
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example, XenAPI for XenServer/XCP, libvirt for KVM or QEMU and
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VMwareAPI for VMware. Processing is fairly complex but fundamentally it
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accepts actions from the queue and performs a series of system
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commands, like launching a KVM instance, whilst updating its state in
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the database.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><systemitem class="service">nova-scheduler</systemitem>
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process</term>
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<listitem><para>Conceptually the simplest piece of code in OpenStack
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Compute. It takes a virtual machine instance request from the queue and
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determines on which compute server host it will run.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><systemitem class="service">nova-conductor</systemitem>
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module</term><listitem><para>Mediates interactions between <systemitem
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class="service">nova-compute</systemitem> and the database.
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It eliminates direct accesses to the cloud database made
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by <systemitem class="service">nova-compute</systemitem>. The
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<systemitem class="service">nova-conductor</systemitem>
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module scales horizontally. However, do not deploy it on any
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nodes where <systemitem class="service"
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>nova-compute</systemitem> runs. For more information, see
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<link
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xlink:href="http://russellbryantnet.wordpress.com/2012/11/19/a-new-nova-service-nova-conductor/"
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>A new Nova service: nova-conductor</link>.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<variablelist><title>Networking for VMs</title>
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<varlistentry><term><systemitem class="service">nova-network</systemitem>
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worker daemon</term>
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<listitem><para>Similar to <systemitem
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class="service">nova-compute</systemitem>, it accepts networking tasks from
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the queue and performs tasks to manipulate the network, such
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as setting up bridging interfaces or changing iptables rules.
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This functionality is being migrated to OpenStack Networking.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><systemitem class="service">nova-dhcpbridge</systemitem>
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script</term>
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<listitem><para>The IP address leases and is recorded in the
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database using the dnsmasq <literal>dhcp-script</literal>
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facility. This functionality is being migrated to OpenStack
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Networkin which provides a different script.</para></listitem>
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</varlistentry>
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</variablelist>
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<?hard-pagebreak?>
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<variablelist><title>Console interface</title>
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<varlistentry>
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<term><systemitem class="service">nova-consoleauth</systemitem>
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daemon</term><listitem><para>Authorizes tokens for users that console
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proxies provide. See <systemitem class="service"
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>nova-novncproxy</systemitem> and <systemitem
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class="service">nova-xvpnvcproxy</systemitem>. This service
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must be running for console proxies to work. Many proxies of
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either type can be run against a single <systemitem
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class="service">nova-consoleauth</systemitem> service in a
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cluster configuration. For information, see <link
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xlink:href="http://docs.openstack.org/trunk/config-reference/content/about-nova-consoleauth.html"
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>About nova-consoleauth</link>.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><systemitem class="service">nova-novncproxy</systemitem>
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daemon</term>
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<listitem><para>Provides a proxy for accessing running instances through
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a VNC connection. Supports browser-based novnc
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clients.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><systemitem class="service">nova-xvpnvncproxy</systemitem>
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daemon</term>
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<listitem><para>A proxy for accessing running instances
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through a VNC connection. It supports a Java client specifically
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designed for OpenStack.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><systemitem class="service">nova-cert</systemitem> daemon</term>
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<listitem><para>x509 certificates.</para></listitem>
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</varlistentry>
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</variablelist>
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<para os="debian">In Debian, a unique
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<package>nova-consoleproxy</package> package provides the
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<package>nova-novncproxy</package>,
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<package>nova-spicehtml5proxy</package>, and
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<package>nova-xvpvncproxy</package> packages. To select
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packages, edit the
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<filename>/etc/default/nova-consoleproxy</filename> file or use
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the <package>debconf</package> interface. You can also manually
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edit the <filename>/etc/default/nova-consoleproxy</filename> file,
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and stop and start the console daemons.</para>
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<variablelist> <title>Image management (EC2 scenario)</title>
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<varlistentry>
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<term><systemitem class="service">nova-objectstore</systemitem>
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daemon</term> <listitem><para>A S3 interface for registering images
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with the OpenStack Image Service. It is mainly used for installations
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that must support euca2ools. The euca2ools tools talk to <systemitem
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class="service">nova-objectstore</systemitem> in <emphasis
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role="italic">S3 language</emphasis>, and <systemitem
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class="service">nova-objectstore</systemitem> translates S3
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requests into Image service requests.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>euca2ools client</term>
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<listitem><para>A set of command-line interpreter commands for managing
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cloud resources. Although it is not an OpenStack module, you can
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configure <systemitem class="service">nova-api</systemitem> to support
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this EC2 interface. For more information, see the <link
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xlink:href="https://www.eucalyptus.com/docs/eucalyptus/3.4/index.html"
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>Eucalyptus 3.4 Documentation</link>.</para></listitem>
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</varlistentry>
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</variablelist>
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<variablelist><title>Command-line clients and other interfaces</title>
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<varlistentry><term>nova client</term>
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<listitem><para>Allows users to submit commands as a tenant administrator
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or end user.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term>nova-manage client</term>
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<listitem><para>Enables cloud administrators to submit
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commands.</para></listitem>
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</varlistentry>
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</variablelist>
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<variablelist><title>Other components</title>
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<varlistentry><term>The queue</term><listitem><para>A central hub for
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passing messages between daemons. It is usually implemented with <link
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xlink:href="http://www.rabbitmq.com/">RabbitMQ</link>, but
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could be any AMQP message queue, such as <link
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xlink:href="http://qpid.apache.org/">Apache Qpid</link> or
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<link xlink:href="http://www.zeromq.org/">Zero
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MQ</link>.</para></listitem>
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</varlistentry>
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<varlistentry><term>SQL database</term>
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<listitem><para>Stores most build-time and runtime states for a cloud
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infrastructure. It includes instance types that are available for use,
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instances in use, available networks, and projects. Theoretically,
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OpenStack Compute can support any database that is supported by SQL-Alchemy.
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Note the databases which are widely used are SQLite3 databases (for test and
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development work), MySQL, and PostgreSQL.</para></listitem>
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</varlistentry>
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</variablelist>
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<para>OpenStack Compute interacts with OpenStack Identity for
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authentication; OpenStack Image Service for images; and the OpenStack
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dashboard for a web interface.</para>
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</section>
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