[OpenStack]架构和基本概念

Architecture

Key Compute API Concepts

• Server

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

• Flavor

  Virtual hardware configuration for the requested 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 at it’s boot time. 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 limit 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 administrator-level action.
  

• Availability zone

  A grouping of host machines that can be used to control where a new server is created.
  

• Hosts

  Hosts are the physical machines that provide the resources for the virtual servers created in Nova.
  They run a hypervisor that handles the actual creation and management of the virtual servers.
  Hosts also run the Nova compute service, which receives requests from Nova to interact with the virtual servers on that machine. When compute service receives a request, it calls the appropriate methods of the driver for that hypervisor in order to carry out the request. The driver acts as the translator from generic Nova requests to hypervisor-specific calls. Hosts report their current state back to Nova, where it is tracked by the scheduler service, so that the scheduler can place requests for new virtual servers on the hosts that can best fit them.
  

• Hypervisors

  A hypervisor, or virtual machine monitor (VMM), is a piece of computer software, firmware or hardware that creates and runs virtual machines.
  In nova, each Host (see Hosts) runs a hypervisor. Administrators are able to query the hypervisor for information, such as all the virtual servers currently running, as well as detailed info about the hypervisor, such as CPU, memory, or disk related configuration.
  

• Migrations

  Migrations are the process where a virtual server is moved from one host to another.
  Administrators are able to query the records in database for information about migrations. For example, they can determine the source and destination hosts, type of migration, or changes in the server’s flavor.