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.

Overview

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:

Services

nova-api-metadata </cli/nova-api-metadata>

A server daemon that serves the Nova Metadata API.

nova-api-os-compute </cli/nova-api-os-compute>

A server daemon that serves the Nova OpenStack Compute API.

nova-api </cli/nova-api>

A server daemon that serves the metadata and compute APIs in separate
greenthreads.

nova-compute </cli/nova-compute>

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

nova-conductor </cli/nova-conductor>

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

nova-scheduler </cli/nova-scheduler>

Dispatches requests for new virtual machines to the correct node.

nova-novncproxy </cli/nova-novncproxy>

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

nova-spicehtml5proxy </cli/nova-spicehtml5proxy>

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

nova-serialproxy </cli/nova-serialproxy>

Provides a serial console proxy, allowing users to access a virtual
machine’s serial console.

The architecture is covered in much greater detail in /admin/architecture.

Deployment Considerations

There is information you might want to consider before doing your
deployment, especially if it is going to be a larger deployment. For
smaller deployments the defaults from the install guide </install/index> will be
sufficient.

• Compute Driver Features Supported: While the
  majority of nova deployments use libvirt/kvm, you can use nova with
  other compute drivers. Nova attempts to provide a unified feature set
  across these, however, not all features are implemented on all backends,
  and not all features are equally well tested.
  • Feature Support by Use Case </user/feature-classification>:
    A view of what features each driver supports based on what’s important
    to some large use cases (General Purpose Cloud, NFV Cloud, HPC
    Cloud).
  • Feature Support full list </user/support-matrix>:
    A detailed dive through features in each compute driver backend.
• Cells v2 configuration </admin/cells>: For large
  deployments, cells v2 cells allow sharding of your compute environment.
  Upfront planning is key to a successful cells v2 layout.
• Availablity Zones </admin/availability-zones>:
  Availability Zones are an end-user visible logical abstraction for
  partitioning a cloud without knowing the physical infrastructure.
• Placement service <>: Overview of the
  placement service, including how it fits in with the rest of nova.
• Running nova-api on wsgi </user/wsgi>:
  Considerations for using a real WSGI container instead of the baked-in
  eventlet web server.

Basic configuration

Once you have an OpenStack deployment up and running, you will want
to manage it. The below guides cover everything from creating initial
flavor and image to log management and live migration of instances.

• Quotas </admin/quotas>: Managing project quotas
  in nova.
• Scheduling </admin/scheduling>: How the
  scheduler is configured, and how that will impact where compute
  instances land in your environment. If you are seeing unexpected
  distribution of compute instances in your hosts, you’ll want to dive
  into this configuration.
• Exposing custom metadata to compute instances </admin/vendordata>:
  How and when you might want to extend the basic metadata exposed to
  compute instances (either via metadata server or config drive) for your
  specific purposes.

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.

Maintenance

Once you are running nova, the following information is extremely
useful.

• Upgrades <upgrades>: How nova is designed to be
  upgraded for minimal service impact, and the order you should do them
  in.