CDN加速后源站本来有的etag字段消失了

详细解答可以参考官方帮助文档

建议排查是否开启了cdn的 gzip功能

因为Nginx的默认行为就是这样，同时开启gzip和etag，就直接不用etag了。以下是Nginx文档原文：

The issue was discussed over several forum threads and trackers. It appeared that Nginx deliberately strips ETags once gzip is applied,The motivation behind was that ETag should serve as a byte-accurate comparison, and since the result of gzip is not guaranteed to be identical under different configurations, ETag is no longer a strong validator and Nginx decided that it was simpler to remove it as opposed to converting it to a weak one.