If there is more back-to-source traffic than access traffic when using the CDN, see the following:
This can occur if the CDN has enabled Gzip compression but the origin site has not.
Gzip has a high compression ratio for content such as text. If the origin site has not enabled Gzip compression but the CDN has, then problems such as CDN back-to-source bandwidth being greater than access bandwidth when user is accessing the CDN would occur. You are advised to enable Gzip on the origin site.
Moreover, some required header information such as a Via header is added when using the CDN. If the origin site has enabled Gzip, see the following:
However, when the request includes the Via header, the origin site may not be able to enable Gzip. See the following:
In this scenario, you are advised to set Gzip as all enabled for the origin site. Take Nginx as an example. If using Nginx, the following settings are recommended:
For using another web service, please follow this modification.