Compute service overview¶

Use OpenStack Compute to host and manage cloud computing systems. OpenStack Compute is a major part of an Infrastructure-as-a-Service (IaaS) system. The main modules are implemented in Python.

OpenStack Compute interacts with OpenStack Identity for authentication; OpenStack Image service for disk and server images; and OpenStack Dashboard for the user and administrative interface. Image access is limited by projects, and by users; quotas are limited per project (the number of instances, for example). OpenStack Compute can scale horizontally on standard hardware, and download images to launch instances.

OpenStack计算服务由下列组件所构成：

``nova-api``服务

接收和响应来自最终用户的计算API请求。此服务支持OpenStack计算服务API，Amazon EC2 API，以及特殊的管理API用于赋予用户做一些管理的操作。它会强制实施一些规则，发起多数的编排活动，例如运行一个实例。

``nova-api-metadata``服务

Accepts metadata requests from instances. The nova-api-metadata service is generally used when you run in multi-host mode with nova-network installations. For details, see Metadata service in the OpenStack Administrator Guide.

``nova-compute``服务

一个持续工作的守护进程，通过Hypervior的API来创建和销毁虚拟机实例。例如：

• XenServer/XCP 的 XenAPI
• KVM 或 QEMU 的 libvirt
• VMware 的 VMwareAPI

过程是蛮复杂的。最为基本的，守护进程同意了来自队列的动作请求，转换为一系列的系统命令如启动一个KVM实例，然后，到数据库中更新它的状态。

nova-placement-api service

Tracks the inventory and usage of each provider. For details, see Placement API.

``nova-scheduler``服务

拿到一个来自队列请求虚拟机实例，然后决定那台计算服务器主机来运行它。

``nova-conductor``模块

Mediates interactions between the nova-compute service and the database. It eliminates direct accesses to the cloud database made by the nova-compute service. The nova-conductor module scales horizontally. However, do not deploy it on nodes where the nova-compute service runs. For more information, see Configuration Reference Guide.

nova-cert 模块

服务器守护进程向Nova Cert服务提供X509证书。用来为``euca-bundle-image``生成证书。仅仅是在EC2 API的请求中使用

nova-consoleauth 模块

Authorizes tokens for users that console proxies provide. See nova-novncproxy and nova-xvpvncproxy. This service must be running for console proxies to work. You can run proxies of either type against a single nova-consoleauth service in a cluster configuration. For information, see About nova-consoleauth.

nova-novncproxy 模块

提供一个代理，用于访问正在运行的实例，通过VNC协议，支持基于浏览器的novnc客户端。

``nova-spicehtml5proxy``守护进程

提供一个代理，用于访问正在运行的实例，通过 SPICE 协议，支持基于浏览器的 HTML5 客户端。

nova-xvpvncproxy 守护进程

提供一个代理，用于访问正在运行的实例，通过VNC协议，支持OpenStack特定的Java客户端。

队列

A central hub for passing messages between daemons. Usually implemented with RabbitMQ, also can be implemented with another AMQP message queue, such as ZeroMQ.

SQL数据库

存储构建时和运行时的状态，为云基础设施，包括有：

• 可用实例类型
• 使用中的实例
• 可用网络
• 项目

Theoretically, OpenStack Compute can support any database that SQLAlchemy supports. Common databases are SQLite3 for test and development work, MySQL, MariaDB, and PostgreSQL.