If multiple IP addresses are added, Alibaba Cloud CDN will poll each IP address. If one server cannot provide services, requests will not be carried back to the faulty server any more.
If multiple IP addresses are added, the Alibaba Cloud CDN backend will check port 80, and the Alibaba Cloud CDN does not access the server corresponding to an IP address only the port 80 cannot be accessed. Therefore, it is possible that an error is prompted when the port 80 can be accessed but the service is not available.
If the problem persists, contact Alibaba Cloud After-Sales Technical Support.