f21b07153d
In a fairly hack and slash fashion, remove the installation of placement from the nova install docs. Placement will have its own installation docs. Configuring access to placement from the controller and compute nodes is still described. The depends-on is to the patch that provides placement install docs. The output of 'nova-status upgrade check' is updated to reflect the current state of the output of that command; this means it now includes a fair bit more than checking cells v2 and the existence of the placement API. Depends-On: https://review.openstack.org/#/c/628220/ Change-Id: I9e082a9c6d4b6369f1ec6c17bbd3ccc417a5e97b
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========================
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Compute service overview
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========================
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.. todo:: Update a lot of the links in here.
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Use OpenStack Compute to host and manage cloud computing systems. OpenStack
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Compute is a major part of an Infrastructure-as-a-Service (IaaS) system. The
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main modules are implemented in Python.
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OpenStack Compute interacts with OpenStack Identity for authentication,
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OpenStack Placement for resource inventory tracking and selection, OpenStack
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Image service for disk and server images, and OpenStack Dashboard for the user
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and administrative interface. Image access is limited by projects, and by
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users; quotas are limited per project (the number of instances, for example).
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OpenStack Compute can scale horizontally on standard hardware, and download
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images to launch instances.
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OpenStack Compute consists of the following areas and their components:
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``nova-api`` service
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Accepts and responds to end user compute API calls. The service supports the
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OpenStack Compute API. It enforces some policies and initiates most
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orchestration activities, such as running an instance.
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``nova-api-metadata`` service
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Accepts metadata requests from instances. The ``nova-api-metadata`` service
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is generally used when you run in multi-host mode with ``nova-network``
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installations. For details, see :ref:`metadata-service-deploy`
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in the Compute Administrator Guide.
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``nova-compute`` service
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A worker daemon that creates and terminates virtual machine instances through
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hypervisor APIs. For example:
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- XenAPI for XenServer/XCP
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- libvirt for KVM or QEMU
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- VMwareAPI for VMware
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Processing is fairly complex. Basically, the daemon accepts actions from the
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queue and performs a series of system commands such as launching a KVM
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instance and updating its state in the database.
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``nova-scheduler`` service
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Takes a virtual machine instance request from the queue and determines on
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which compute server host it runs.
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``nova-conductor`` module
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Mediates interactions between the ``nova-compute`` service and the database.
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It eliminates direct accesses to the cloud database made by the
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``nova-compute`` service. The ``nova-conductor`` module scales horizontally.
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However, do not deploy it on nodes where the ``nova-compute`` service runs.
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For more information, see the ``conductor`` section in the
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:doc:`/configuration/config`.
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``nova-consoleauth`` daemon
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Authorizes tokens for users that console proxies provide. See
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``nova-novncproxy`` and ``nova-xvpvncproxy``. This service must be running
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for console proxies to work. You can run proxies of either type against a
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single nova-consoleauth service in a cluster configuration. For information,
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see :ref:`about-nova-consoleauth`.
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.. deprecated:: 18.0.0
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``nova-consoleauth`` is deprecated since 18.0.0 (Rocky) and will be removed
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in an upcoming release. See
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:oslo.config:option:`workarounds.enable_consoleauth` for details.
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``nova-novncproxy`` daemon
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Provides a proxy for accessing running instances through a VNC connection.
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Supports browser-based novnc clients.
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``nova-spicehtml5proxy`` daemon
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Provides a proxy for accessing running instances through a SPICE connection.
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Supports browser-based HTML5 client.
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``nova-xvpvncproxy`` daemon
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Provides a proxy for accessing running instances through a VNC connection.
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Supports an OpenStack-specific Java client.
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.. deprecated:: 19.0.0
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:program:`nova-xvpvnxproxy` is deprecated since 19.0.0 (Stein) and will be
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removed in an upcoming release.
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The queue
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A central hub for passing messages between daemons. Usually implemented with
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`RabbitMQ <https://www.rabbitmq.com/>`__, also can be implemented with
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another AMQP message queue, such as `ZeroMQ <http://www.zeromq.org/>`__.
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SQL database
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Stores most build-time and run-time states for a cloud infrastructure,
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including:
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- Available instance types
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- Instances in use
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- Available networks
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- Projects
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Theoretically, OpenStack Compute can support any database that SQLAlchemy
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supports. Common databases are SQLite3 for test and development work, MySQL,
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MariaDB, and PostgreSQL.
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