Target upstream services

Cloud CDN can have only GCP load balancer as the upstream services. And GCP load balancer can configure one of followings for backends.

1. Backend services
   1. GCE instance groups
   2. GCE Network endpoint groups. These are the groups of VM instances
2. Backend buckets

See official document for the architecture using this.

Configurations

Cache can be controlled by response headers of origin servers, like cache expiration times, like Cache-Control: max-age header. The details are described in here.

Reference

Cloud CDN