CDN bills requests based on the number of log entries recorded at the application layer (Layer 7). Every request that reaches and is processed by a point of presence (POP) counts as one billable request — including failed requests that don't return the resource, because the POP still parses them at the application layer.
Is a client-cached file request charged again?
Yes. When a client already has the file cached, the POP detects that the file is cached and not updated, then returns an HTTP 304 (Not Modified) status code. The request is still counted as one billable request. A small amount of data transfer is also generated because the POP sends a response packet back to the client. The exact fee depends on the protocol used.
Am I charged for requests from attackers?
Yes. CDN mitigates attacks at the application layer, which consumes resources and generates fees. How much you're charged depends on whether the IP address blacklist or whitelist is enabled:
| IP blacklist/whitelist | Effect on billing |
|---|---|
| Disabled | All attack requests reach the POP and are billed. Fees for requests and data transfer can be significant. |
| Enabled | Requests from blocked IPs are blocked. The number of billable requests and data transfer are significantly reduced. |
To reduce fees from attack traffic, enable the IP address blacklist or whitelist. See Configure an IP address blacklist or whitelist.