https://developer.aliyun.com/article/608417
https://developer.aliyun.com/ask/56280
什么是CDN？
https://www.alibabacloud.com/help/zh/doc-detail/27101.htm?spm=a2c63.p38356.b99.5.5ee54befv3mBMR
CDN学习路径：
https://www.alibabacloud.com/zh/getting-started/learningpath/cdn
CDN收费：
