nova/api-guide/source/general_info.rst

Key Compute API Concepts

The OpenStack Compute API is defined as a ReSTful HTTP service. The API takes advantage of all aspects of the HTTP protocol (methods, URIs, media types, response codes, etc.) and providers are free to use existing features of the protocol such as caching, persistent connections, and content compression among others.

Providers can return information identifying requests in HTTP response headers, for example, to facilitate communication between the provider and client users.

OpenStack Compute is a compute service that provides server capacity in the cloud. Compute Servers come in different flavors of memory, cores, disk space, and CPU, and can be provisioned in minutes. Interactions with Compute Servers can happen programmatically with the OpenStack Compute API.

User Concepts

To use the OpenStack Compute API effectively, you should understand several key concepts:

• Server

  A virtual machine (VM) instance in the compute system. Flavor and image are requisite elements when creating a server. A name for the server is also required.

  For more details, such as server actions and server metadata, please see: server_concepts

• Flavor

  An available hardware configuration for a server. Each flavor has a unique combination of disk space, memory capacity and priority for CPU time.

• Image

  A collection of files used to create or rebuild a server. Operators provide a number of pre-built OS images by default. You may also create custom images from cloud servers you have launched. These custom images are useful for backup purposes or for producing “gold” server images if you plan to deploy a particular server configuration frequently.

• Key Pair

  An ssh or x509 keypair that can be injected into a server. This allows you to connect to your server once it has been created without having to use a password. If you don't specify a key pair, Nova will create a root password for you, and return it in plain text in the server create response.

• Volume

  A block storage device that Nova can use as permanent storage. When a server is created it has some disk storage available, but that is considered ephemeral, as it is destroyed when the server is destroyed. A volume can be attached to a server, then later detached and used by another server. Volumes are created and managed by the Cinder service, though the Nova API can proxy some of these calls.

• Quotas

  An upper bound on the amount of resources any individual tenant may consume. Quotas can be used to limit the number of servers a tenant creates, or the amount of disk space consumed, so that no one tenant can overwhelm the system and prevent normal operation for others. Changing quotas is an admin-level action.

• Rate Limiting

  Please see limits

• Availability zone

  A grouping of host machines that can be used to control where a new server is created. There is some confusion about this, as the name "availability zone" is used in other clouds, such as Amazon Web Services, to denote a physical separation of server locations that can be used to distribute cloud resources for fault tolerance in case one zone is unavailable for any reason. Such a separation is possible in Nova if an admin carefully sets up availability zones for that, but it is not the default.

Networking Concepts

In this section we focus on this related to networking.

• Port

  TODO

• Floating IPs, Pools and DNS

  TODO

• Security Groups

  TODO

• Cloudpipe

  TODO

• Extended Networks

  TODO

Administrator Concepts

Come APIs are largely focused on administration of Nova, and generally focus on compute hosts rather than servers.

• Hosts

  TODO

• Host Actions

  TODO

• Hypervisors

  TODO

• Aggregates

  TODO

• Migrations

  TODO

• Certificates

  TODO

Error Handling

The Compute API follows the standard HTTP error code conventions.

TODO - add details including: request id, migrations and instance actions.

Relationship with Volume API

Here we discuss about Cinder's API and how Nova users volume uuids.

TODO - add more details.

Relationship with Image API

Here we discuss about Glance's API and how Nova users image uuids. We also discuss how Nova proxies setting image metadata.

TODO - add more details.

Interactions with Neutron and Nova-Network

We talk about how networking can be provided be either by Nova or Neutron.

Here we discuss about Neutron's API an how Nova users port uuids. We also discuss Nova automatically creating ports, proxying security groups, and proxying floating IPs. Also talk about the APIs we do not proxy.

TODO - add more details.