Compute service overview

Todo

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 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. It enforces some policies and initiates most orchestration activities, such as running an instance.

nova-api-metadata service

Accepts metadata requests from instances. For more information, refer to Metadata service.

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 the conductor section in the Configuration Options.

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.

Deprecated since version 19.0.0: nova-xvpvnxproxy is deprecated since 19.0.0 (Stein) and will be removed in an upcoming release.

The queue

A central hub for passing messages between daemons. Usually implemented with RabbitMQ but other options are available.

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.