1. A computer-implemented method, in a content delivery (CD) network comprising multiple CD service endpoints, said CD service endpoints running on a plurality of devices, the method operable on a device comprising hardware including memory and at least one processor, the method comprising: (A) defining a first group from a first arbitrary set of nodes comprising CD service instances across the machines of one or more sub-clusters of said CD network (CDN), wherein each node in the first group assumes one or more discrete responsibilities involved in processing of a request across the first group, wherein, in response to a request made at a node of the first group, one or more nodes in said first group is selected to be responsible for processing of the request, said first group having a first topology; and (B) in response to a change to a particular node in said CDN, (B)(1) defining a second group from a second arbitrary set of nodes comprising CD service instances across the machines of said one or more sub-clusters of said CDN, wherein each node in the second group assumes one or more discrete responsibilities involved in processing of a request across the second group, wherein, in response to a request made at a node of the second group, one or more nodes in said second group is selected to be responsible for processing of the request, said second group having a second topology distinct from said first topology; and (B)(2) transitioning request processing from the first group to the second group over a time period based on a responsibility adaptation policy, wherein said time period comprises a fade interval, and wherein nodes in both said first group and said second group share a particular responsibility for request processing during the time period, wherein said responsibility adaptation policy uses a fading function that fades to zero over said fade interval.