1.Windows Azure's Service Management Versioning
Operations provided by the Service Management API may have multiple versions. You must specify the version of an operation that you want to use by setting the x-ms-version request header. Requests without an x-ms-version header will be rejected and return a (400) Bad Request response. If your service calls an older version of an operation, you can choose to continue calling the older version, or modify your code to call a newer version. Any differences in functionality between versions are outlined in the documentation for the API call.
注:
Windows Azure是一个公有平台，所以为了满足不同版本的应用提供了不同版本的API,那么如何去告诉Http请求调用哪一个版本的API呢?上面说设置请求头的x-ms-version参数。不管你是老版本的还是新版本的，只要你设置了请求头的x-ms-version参数就可以根据设置的参数调用相应的API.
The x-ms-version request header value must be specified in the format YYYY-MM-DD.
For example:
Request Headers: x-ms-version: 2011-02-25
总结:
云平台是一个公共服务的平台，所以需要保留各个版本的API以满足所有企业和个人的应用调用需要，同时更好的满足应用的升级和扩展，调用时只要在请求头中将x-ms-version参数进行赋值，以便知道用那一个版本的API。