Alibaba Cloud CDN and other Alibaba Cloud services—such as Object Storage Service (OSS) and Elastic Compute Service (ECS)—bill for their own outbound traffic separately. Charges from one service do not offset or replace charges from the other.
When a client requests a resource, one of two scenarios determines which services charge fees:
Cache miss — the point of presence (POP) does not have the resource cached
The POP retrieves the resource from the origin (for example, an OSS bucket). OSS charges for the outbound traffic from the bucket to the POP. CDN does not charge at this stage. CDN then delivers the resource from the POP to the client and charges for that outbound traffic. Both OSS and CDN charges appear on your bill for a single cache-miss request.
Cache hit — the resource is already cached on the POP
CDN delivers the resource directly from the POP to the client. OSS is not involved and does not charge. Only CDN outbound traffic fees apply.
When CDN accelerates delivery of resources stored in OSS, the OSS outbound traffic generated during origin fetch is billed at a discounted price. For details, see the billing documentation for Alibaba Cloud CDN and OSS.