1. A computer-implemented method operable in a content delivery network (CDN), and operable on a device comprising hardware including memory and at least one processor comprising: (A) receiving a request for a CDN service of a particular type, wherein a CDN service of said particular type defines a fixed number of configurable layers of request processing, sequentially from a first layer to a last layer; (B) processing said request, starting at said first layer, said processing being based on a modifiable runtime environment, said processing continuing conditionally through each of said layers in turn until either said request is terminated by one of said layers or said last layer processes said request.