In this paper we describe Quorum: a new non-invasive software approachto scalable quality-of-service provisioning that uses traffic shaping,admission control, and response monitoring at the borders of theInternet hosting site to ensure throughput andresponse time guarantees. Quorum treats the cluster and the servicesit is hosting as an unknown ``black-box\'\' system and usesfeedback-driven techniques to dynamically control how and when eachof the requests from the clients must be forwarded into the cluster.We compare Quorum both to over-provisioning and to Neptune -- aresearch and now commercially successful middleware system thatimplements QoS for Internet services. Our results show that Quorumcan enforce the same QoS guarantees as Neptune for Neptune-enabledservices, but without requiring the additional development overheadrequired by Neptune. We also detail Quorum\'s flexibility by using itto provide QoS guarantees for an Internet service benchmark thatis not ready to be used with Neptune or any other invasive softwareapproach. In this case, Quorum achieves the same results aover-provisioning (which is the only other feasible solution) usingone-half of the site resources.