When Alibaba Cloud CDN is configured with IP addresses of multiple origin sites, Alibaba Cloud CDN will poll these IP addresses during origin site access. For this reason, you need to ensure that the different origin sites have consistent content.
Alibaba Cloud CDN implements port-based health check on origin sites. The detection interval is 5s. When Alibaba Cloud CDN detects a port abnormality on an origin site server, it will not send back-to-source requests to the server.
If the problem persists, contact Alibaba Cloud After-Sales Technical Support.