Nova系统架构
Nova is built on a shared-nothing, messaging-based architecture. All of the major nova components can be run on multiple servers. This means that most component to component communication must go via message queue. In order to avoid blocking each component while waiting for a response, we use deferred objects, with a callback that gets triggered when a response is received.
Nova建立在一个无共享，基于消息的架构。所有的nova主要组件都可以运行在不同的服务器。这就意味着大多数组件之间的通信必须通过消息队列。为了避免每个组件在等待响应时的阻塞，我们是用deferred对象，当一个响应接收时会触发相应的回调。
Nova recently moved to using a sql-based central database that is shared by all components in the system. The amount and depth of the data fits into a sql database quite well. For small deployments this seems like an optimal solution. For larger deployments, and especially if security is a concern, nova will be moving towards multiple data stores with some kind of aggregation system.
Nova最近正在迁移到一个基于SQL的中心数据库，系统中所有组件都共享一个数据库。大量的深度的数据非常适合存放在SQL数据库中。对于小型部署，这是一个最佳方案。对于大型部署，特别是非常看重安全的话，nova也将会进一步搬到不同集成系统中的多种数据库。
组件
下面将看到两种不同的架构：
- DB: 基于SQL的数据存储
- API: 组件接收HTTP请求，可以通过osl.messaging和HTTP来转换指令和通信
- Scheduler: 决定哪个host获得某个instance
- Network: 管理IP转发、网桥、vlans
- Compute: 管理hypervisor和virtual machines的通信
- Conductor: 处理需要调整(build/resize)的请求，作为数据库代理，或者处理对象的转换
While all services are designed to be horizontally scalable, you should have significantly more computes then anything else.
由于所有的服务都被设计为横向扩展的，你只需要更多的计算机就可以了。
