openstack/nova
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nova/doc/source/install/get-started-compute.rst
Stephen Finucane 5da2dc2060 setup: Remove pbr's wsgi_scripts 
This is technical dead end and not something we're going to be able to
support long-term in pbr. We need to push users away from this. Doing so
highlights quite a few place where our docs need some work, particularly
in light of the recent removal of the eventlet servers.

Change-Id: I2ffaed710fac2612f5337aca5192af15eab46861
Signed-off-by: Stephen Finucane <stephenfin@redhat.com>
2025-11-04 16:11:50 +00:00

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Compute service overview

Update a lot of the links in here.

Use OpenStack Compute to host and manage cloud computing systems. OpenStack Compute is a major part of an Infrastructure-as-a-Service (IaaS) system. The main modules are implemented in Python.

OpenStack Compute interacts with OpenStack Identity for authentication, OpenStack Placement for resource inventory tracking and selection, 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 two WSGI </admin/wsgi> APIs and a number of services:

Compute API

Accepts and responds to end user compute API calls. The service supports the OpenStack Compute API. It enforces some policies and initiates most orchestration activities, such as running an instance.

Metadata API

Accepts metadata requests from instances. For more information, refer to /admin/metadata-service.

nova-compute service

A worker daemon that creates and terminates virtual machine instances through hypervisor APIs. The default hypervisor is libvirt with KVM or QEMU, but other hypervisors are supported.

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 the conductor section in the /configuration/config.

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.

The queue

A central hub for passing messages between daemons. Usually implemented with RabbitMQ but :oslo.messaging-doc:other options are available <admin/drivers>.

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 SQLAlchemy supports. Common databases are SQLite3 for test and development work, MySQL, MariaDB, and PostgreSQL.

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