The OpenStack Compute service allows you to control an Infrastructure-as-a-Service (IaaS) cloud computing platform. It gives you control over instances and networks, and allows you to manage access to the cloud through users and projects.

Compute does not include virtualization software. Instead, it defines drivers that interact with underlying virtualization mechanisms that run on your host operating system, and exposes functionality over a web-based API.


To effectively administer compute, you must understand how the different installed nodes interact with each other. Compute can be installed in many different ways using multiple servers, but generally multiple compute nodes control the virtual servers and a cloud controller node contains the remaining Compute services.

The Compute cloud works using a series of daemon processes named nova-* that exist persistently on the host machine. These binaries can all run on the same machine or be spread out on multiple boxes in a large deployment. The responsibilities of services and drivers are:



Receives XML requests and sends them to the rest of the system. A WSGI app routes and authenticates requests. Supports the OpenStack Compute APIs. A nova.conf configuration file is created when Compute is installed.


Describe nova-api-metadata, nova-api-os-compute, nova-serialproxy and nova-spicehtml5proxy

nova-console, nova-dhcpbridge and nova-xvpvncproxy are all deprecated for removal so they can be ignored.


Manages virtual machines. Loads a Service object, and exposes the public methods on ComputeManager through a Remote Procedure Call (RPC).


Provides database-access support for compute nodes (thereby reducing security risks).


Dispatches requests for new virtual machines to the correct node.


Provides a VNC proxy for browsers, allowing VNC consoles to access virtual machines.


Some services have drivers that change how the service implements its core functionality. For example, the nova-compute service supports drivers that let you choose which hypervisor type it can use.

Advanced configuration

OpenStack clouds run on platforms that differ greatly in the capabilities that they provide. By default, the Compute service seeks to abstract the underlying hardware that it runs on, rather than exposing specifics about the underlying host platforms. This abstraction manifests itself in many ways. For example, rather than exposing the types and topologies of CPUs running on hosts, the service exposes a number of generic CPUs (virtual CPUs, or vCPUs) and allows for overcommitting of these. In a similar manner, rather than exposing the individual types of network devices available on hosts, generic software-powered network ports are provided. These features are designed to allow high resource utilization and allows the service to provide a generic cost-effective and highly scalable cloud upon which to build applications.

This abstraction is beneficial for most workloads. However, there are some workloads where determinism and per-instance performance are important, if not vital. In these cases, instances can be expected to deliver near-native performance. The Compute service provides features to improve individual instance for these kind of workloads.


In deployments older than Train, or in mixed Stein/Train deployments with a rolling upgrade in progress, unless specifically enabled, live migration is not possible for instances with a NUMA topology when using the libvirt driver. A NUMA topology may be specified explicitly or can be added implicitly due to the use of CPU pinning or huge pages. Refer to bug #1289064 for more information. As of Train, live migration of instances with a NUMA topology when using the libvirt driver is fully supported.

Additional guides