1. A computer-implemented method for dynamically scaling server capacity of a first content delivery network (CDN) participating in a federation of a plurality of CDNs by leveraging server capacity of at least a second CDN from the plurality of CDNs, the computer-implemented method comprising: serving first CDN customer content over a data network to a plurality of end users in a first set of geographic regions exclusively from a first set of content delivery servers operated by the first CDN; serving second CDN customer content over the data network to a plurality of end users in a different second set of geographic regions exclusively from a different second set of content delivery servers the second CDN operates independent of the first set of content delivery servers operated by the first CDN; identifying at the first CDN, (i) a particular geographic region of the first set of geographic regions underserved by the first set of content delivery servers and (ii) an amount of server capacity needed in the particular geographic region by the first CDN from one or more content delivery servers operated by at least one other CDN; querying by the first CDN, a federation exchange comprising a plurality of server capacity instances offered by different CDNs of the plurality of CDNs with each server capacity instance being associated with at least one geographic region and an amount of server capacity provided by one or more content delivery servers operated by a CDN participating in the federation, wherein querying the exchange identifies a server capacity instance offered by the second CDN, wherein the second CDN offered server capacity instance provides the amount of server capacity to the particular geographic region needed by the first CDN from one or more content delivery servers operated by the second CDN; deploying from the first CDN, a customer configuration for a particular customer of the first CDN to the server capacity of the second CDN identified in the server capacity instance as a result of said querying, said deploying comprising configuring the one or more content delivery servers of the second CDN server capacity instance with the customer configuration of the particular customer of the first CDN; serving content of the first CDN particular customer over the data network to the particular geographic region from the one or more content delivery servers of the second CDN server capacity instance while simultaneously serving content of the first CDN particular customer over the data network to other geographic regions from the first set of content delivery servers of the first CDN; and providing at the first CDN, an interface from which the customer of the first CDN (i) modifies said customer configuration after deployment to the server capacity of the one or more content delivery servers operated by the second CDN and (ii) views content caching and serving performance results to the particular geographic region of said customer configuration after running on the server capacity of the one or more content delivery servers operated by the second CDN for some time, wherein said interface is not operated by the second CDN.