openstack-manuals/doc/common/get_started_compute.rst
Gauvain Pocentek 52d0cfb940 [config-ref] Remove references to Qpid
The support has been dropped from Oslo, don't suggest it is still
usable.

Change-Id: I2ec090b5f093bbf45d19210bf07fe302ad8e07ba
2016-03-19 16:32:34 +01:00

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=================
OpenStack Compute
=================
Use OpenStack Compute to host and manage cloud computing systems.
OpenStack Compute is a major part of an Infrastructure-as-a-Service
(:term:`IaaS`) system. The main modules are implemented in Python.
OpenStack Compute interacts with OpenStack Identity for authentication;
OpenStack Image service for disk and server images; and OpenStack
dashboard for the user and administrative interface. Image access is
limited by projects, and by users; quotas are limited per project (the
number of instances, for example). OpenStack Compute can scale
horizontally on standard hardware, and download images to launch
instances.
OpenStack Compute consists of the following areas and their components:
``nova-api`` service
Accepts and responds to end user compute API calls. The service
supports the OpenStack Compute API, the Amazon EC2 API, and a
special Admin API for privileged users to perform administrative
actions. It enforces some policies and initiates most orchestration
activities, such as running an instance.
``nova-api-metadata`` service
Accepts metadata requests from instances. The ``nova-api-metadata``
service is generally used when you run in multi-host mode with
``nova-network`` installations. For details, see `Metadata
service <http://docs.openstack.org/admin-guide-cloud/compute-networking-nova.html#metadata-service>`__
in the OpenStack Cloud Administrator Guide.
``nova-compute`` service
A worker daemon that creates and terminates virtual machine
instances through hypervisor APIs. For example:
- XenAPI for XenServer/XCP
- libvirt for KVM or QEMU
- VMwareAPI for VMware
Processing is fairly complex. Basically, the daemon accepts actions
from the queue and performs a series of system commands such as
launching a KVM instance and updating its state in the database.
``nova-scheduler`` service
Takes a virtual machine instance request from the queue and
determines on which compute server host it runs.
``nova-conductor`` module
Mediates interactions between the ``nova-compute`` service and the
database. It eliminates direct accesses to the cloud database made
by the ``nova-compute`` service. The ``nova-conductor`` module scales
horizontally. However, do not deploy it on nodes where the
``nova-compute`` service runs. For more information, see `Configuration
Reference Guide <http://docs.openstack.org/liberty/config-reference/content/
section_conductor.html>`__.
``nova-cert`` module
A server daemon that serves the Nova Cert service for X509
certificates. Used to generate certificates for
``euca-bundle-image``. Only needed for the EC2 API.
``nova-network worker`` daemon
Similar to the ``nova-compute`` service, accepts networking tasks from
the queue and manipulates the network. Performs tasks such as
setting up bridging interfaces or changing IPtables rules.
``nova-consoleauth`` daemon
Authorizes tokens for users that console proxies provide. See
``nova-novncproxy`` and ``nova-xvpvncproxy``. This service must be running
for console proxies to work. You can run proxies of either type
against a single nova-consoleauth service in a cluster
configuration. For information, see `About
nova-consoleauth <http://docs.openstack.org/admin-guide-cloud/compute-remote-console-access.html#about-nova-consoleauth>`__.
``nova-novncproxy`` daemon
Provides a proxy for accessing running instances through a VNC
connection. Supports browser-based novnc clients.
``nova-spicehtml5proxy`` daemon
Provides a proxy for accessing running instances through a SPICE
connection. Supports browser-based HTML5 client.
``nova-xvpvncproxy`` daemon
Provides a proxy for accessing running instances through a VNC
connection. Supports an OpenStack-specific Java client.
``nova-cert`` daemon
x509 certificates.
``euca2ools`` client
A set of command-line interpreter commands for managing cloud
resources. Although it is not an OpenStack module, you can configure
nova-api to support this EC2 interface. For more information, see
the `Eucalyptus 3.4
Documentation <https://www.eucalyptus.com/docs/eucalyptus/3.4/index.html>`__.
``nova`` client
Enables users to submit commands as a tenant administrator or end
user.
The queue
A central hub for passing messages between daemons. Usually
implemented with `RabbitMQ <http://www.rabbitmq.com/>`__, but can be
implemented with an AMQP message queue, such as `Zero
MQ <http://www.zeromq.org/>`__.
SQL database
Stores most build-time and run-time states for a cloud
infrastructure, including:
- Available instance types
- Instances in use
- Available networks
- Projects
Theoretically, OpenStack Compute can support any database that
SQL-Alchemy supports. Common databases are SQLite3 for test and
development work, MySQL, and PostgreSQL.