openstack-nova源码分析(六）availability_zone 可用区

Availability zones (os-availability-zone)
可用区 在openstack中并没有很明确的定义
注： Openstack 对于可用区的定义可能跟一些可用区定义不一样，只以openstack做分析
官方将解释为主机的聚合（Host Aggregates）， 可用区在openstack中没有相应的表定义，创建更新接口则使用Host Aggregates功能，
主机组可以被认为是可用区的进一步划分，主机组只对管理员可见而可用区用户可见
然而，主机组与可用区并不是同一个概念
可用区是主机的metadata 的一组聚合
注：
1.一个主机可以属于多个主机组，但是只能属于一个可用区
2.主机默认属于default可用区，即使主机不属于任何主机组

Lists and gets detailed availability zone information.
An availability zone is created or updated by setting the availability_zone parameter 
in the create, update, or create or update methods of the Host Aggregates API. 
See Host Aggregates for more details.

官方解释为：

Host aggregates can be regarded as a mechanism to further partition an availability zone; 
while availability zones are visible to users, host aggregates are only visible to administrators

Availability Zones are the end-user visible logical abstraction for partitioning a cloud without knowing the physical infrastructure. 
That abstraction doesn’t come up in Nova with an actual database model since the availability zone is actually a specific metadata information 
attached to an aggregate. Adding that specific metadata to an aggregate makes the aggregate visible from an end-user perspective and consequently 
allows to schedule upon a specific set of hosts (the ones belonging to the aggregate).
That said, there are a few rules to know that diverge from an API perspective between aggregates and availability zones:
1.one host can be in multiple aggregates, but it can only be in one availability zone
2. by default a host is part of a default availability zone even if it doesn’t belong to an aggregate (the configuration option is named default_availability_zone)

一. url及命令行

1. url
   url只有GET 获取列表的方法 ：

/os-availability-zone
/os-availability-zone/detail

2. 命令行

nova availability-zone-list

二. 源码

availability_zone = nova.api.opensta