111 lines
5.5 KiB
XML
111 lines
5.5 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE section [
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<!-- Some useful entities borrowed from HTML -->
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<!ENTITY ndash "–">
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<!ENTITY mdash "—">
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<!ENTITY hellip "…">
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<!ENTITY plusmn "±">
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<!-- Useful for describing APIs -->
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<!ENTITY GET '<command xmlns="http://docbook.org/ns/docbook">GET</command>'>
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<!ENTITY PUT '<command xmlns="http://docbook.org/ns/docbook">PUT</command>'>
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<!ENTITY POST '<command xmlns="http://docbook.org/ns/docbook">POST</command>'>
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<!ENTITY DELETE '<command xmlns="http://docbook.org/ns/docbook">DELETE</command>'>
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]>
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<section xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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xmlns:svg="http://www.w3.org/2000/svg"
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xmlns:m="http://www.w3.org/1998/Math/MathML"
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xmlns:html="http://www.w3.org/1999/xhtml"
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xmlns:db="http://docbook.org/ns/docbook" version="5.0"
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xml:id="concepts">
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<?dbhtml stop-chunking?>
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<title>Concepts</title>
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<para>To use the OpenStack Compute API effectively, you should
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understand several key concepts:</para>
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<itemizedlist>
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<listitem>
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<para><emphasis role="bold">Server</emphasis></para>
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<para>A virtual machine (VM) instance in the compute
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system. Flavor and image are requisite elements when
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creating a server.</para>
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</listitem>
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<listitem>
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<para><emphasis role="bold">Flavor</emphasis></para>
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<para>An available hardware configuration for a server.
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Each flavor has a unique combination of disk space,
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memory capacity and priority for CPU time.</para>
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</listitem>
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<listitem>
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<para><emphasis role="bold">Image</emphasis></para>
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<para>A collection of files used to create or rebuild a
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server. Operators provide a number of pre-built OS
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images by default. You may also create custom images
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from cloud servers you have launched. These custom
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images are useful for backup purposes or for producing
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“gold” server images if you plan to deploy a
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particular server configuration frequently.</para>
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</listitem>
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<listitem>
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<para><emphasis role="bold">Reboot
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action</emphasis></para>
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<para>Performs a soft or hard reboot of a server. With a
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soft reboot, the operating system is signaled to
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restart, which allows for a graceful shutdown of all
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processes. A hard reboot is the equivalent of power
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cycling the server. The virtualization platform should
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ensure that the reboot action has completed
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successfully even in cases in which the underlying
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domain/VM is paused or halted/stopped.</para>
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</listitem>
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<listitem>
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<para><emphasis role="bold">Rebuild
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action</emphasis></para>
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<para>Removes all data on the server and replaces it with
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the specified image. Server ID and IP addresses remain
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the same.</para>
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</listitem>
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<listitem>
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<para><emphasis role="bold">Resize
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action</emphasis></para>
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<para>Converts an existing server to a different flavor,
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in essence, scaling the server up or down. The
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original server is saved for a period of time to allow
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rollback if there is a problem. All resizes should be
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tested and explicitly confirmed, at which time the
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original server is removed. All resizes are
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automatically confirmed after 24 hours if you do not
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confirm or revert them.</para>
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</listitem>
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<listitem>
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<para><emphasis role="bold">Pause action</emphasis></para>
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<para>Pauses a server and causes it to run in a frozen
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state. To pause a server, make a <link
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xlink:href="http://docs.openstack.org/api/openstack-compute/2/content/POST_os-admin-actions-v2_pause__v2__tenant_id__servers__server_id__action_ext-action.html"
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>Pause server</link> request. This request stores
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the state of the VM in RAM.</para>
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</listitem>
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<listitem>
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<para><emphasis role="bold">Suspend
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action</emphasis></para>
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<para>Suspends a server, which stores its VM state on
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disk, writes all memory to disk, and stops the virtual
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machine. Suspending an instance is similar to placing
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a device in hibernation; memory and vCPUs become
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available to create other instances. Administrative
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users might want to suspend an infrequently used
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instance or suspend an instance to perform system
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maintenance.</para>
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</listitem>
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<listitem>
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<para><emphasis role="bold">Unpause
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action</emphasis></para>
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<para>Unpauses a paused server. To unpause a server, make
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an <link
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xlink:href="http://docs.openstack.org/api/openstack-compute/2/content/POST_os-admin-actions-v2_unpause__v2__tenant_id__servers__server_id__action_ext-action.html"
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>Unpause server</link> request.</para>
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</listitem>
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</itemizedlist>
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</section>
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