1. A computer-implemented method comprising: obtaining, by a content delivery network (CDN) service provider, at a first DNS server a DNS query from a client computing device, wherein the DNS query corresponds to a requested resource and wherein the DNS query is associated with an original resource identifier which corresponds to a uniform resource locator; identifying, by the first DNS server, first and second alternative DNS servers operative to receive DNS queries; determining, by the first DNS server, a calculated maximum distance between the first alternative DNS server and a reference node, the calculated maximum distance determined based at least in part on a latency time between the first alternative DNS server and the reference node; determining, by the first DNS server, a calculated maximum distance between the second alternative DNS server and the reference node, the calculated maximum distance determined based at least in part on a latency time between the second alternative DNS server and the reference node; identifying, by the first DNS server, a threshold maximum distance radially in any direction from the reference node; determining, by the first DNS server, that the calculated maximum distance between the first alternative server and the reference node does not exceed the threshold maximum distance; determining by the first DNS server, that the calculated maximum distance between the second alternative server and the reference node does not exceed the threshold maximum distance; identifying, by the first DNS server, the first and second alternative servers as members of a set of available alternative DNS servers based on the determinations, for each of the first and second alternative DNS servers, that the respective calculated maximum distance does not exceed the threshold maximum distance; and selecting, by the first DNS server, one of the available alternative DNS servers from the set as a source for the requested resource corresponding to the DNS query, wherein the selected one of the available alternative DNS servers is associated with an alternative resource identifier, wherein the original resource identifier includes information identifying a first domain corresponding to the CDN service provider, and wherein the alternative resource identifier includes information identifying a second domain corresponding to the CDN service provider.