关于Horizon的设计理念：
来自官网（http://docs.openstack.org/developer/horizon/intro.html）：
Horizon holds several key values at the core of its design and architecture:
Core Support: Out-of-the-box support for all core OpenStack projects.
Extensible: Anyone can add a new component as a “first-class citizen”.
Manageable: The core codebase should be simple and easy-to-navigate.
Consistent: Visual and interaction paradigms are maintained throughout.
Stable: A reliable API with an emphasis on backwards-compatibility.
Usable: Providing an awesome interface that people want to use.
The only way to attain and uphold those ideals is to make it easy for developers to implement those values.
官网中特别强调了一句话：
At its core, Horizon should be a registration pattern for applications to hook into
Horizon要像积木一样，(除了Core以外的)应用是可拔插的。灵活，看上去也Cool。
来看下Horizon的结构：
This project is a bit different from other OpenStack projects in that it has two very distinct components underneath it: horizon, and openstack_dashboard.
The horizon directory holds the generic libraries and components that can be used in any Django project.
The openstack_dashboard directory contains a reference Django project that uses horizon.
Horizon的设计基于Django框架，遵循DRY原则。
首先我们先看看 horizon/ 这个目录。horizon这个目录包括了具体应用可能需要用到的公共组件，如table,form等等。
另外一个重要的目录就是 openstack_dashboard/ 这个目录，具体的应用视图是定义在这个目录下的，比如networks的dashboard目录就是 openstack_dashboard/project/networks/ ，每个具体应用的目录结构跟django的app结构相似：
project/
|---__init__.py
|---dashboard.py <-----Registers the app with Horizon and sets dashboard properties
|---overview/
|---images/
|-- images
|-- __init__.py
|---panel.py <-----Registers the panel in the app and defines panel properties
|-- snapshots/
|-- templates/
|-- tests.py
|-- urls.py
|-- views.py
...
...
其他细节，等需要用到在详细介绍。