43f91a87cb
The metadata service docs were hard to find since they were nested down in some nova-network admin guide docs, and they were a mix of end user and admin deployment guide information. This change splits out the end-user facing content into a user guide and leaves the deployment-specific information in the admin guide, and links are updated appropriately. The admin guide portion also referenced some config options that no longer exist, so those are also removed and vendordata_providers is added with a link to the vendordata guide. The options themselves are cleaned up for their current groups and linked to the config option docs. Change-Id: I66035366f3a7ca62ea12d6afa74d13db01ec9f8d
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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 Image service for disk and server images; and OpenStack Dashboard for
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the user and administrative interface. Image access is limited by projects, and
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by users; quotas are limited per project (the number of instances, for
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example). OpenStack Compute can scale horizontally on standard hardware, and
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download 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-placement-api`` service
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Tracks the inventory and usage of each provider. For details, see
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:doc:`/user/placement`.
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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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``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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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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