A proxy server and a hierarchical network system and a distributed workload management method. According to one embodiment of this disclosure, the proxy server includes: a rate controller configured to, based on measured request-related information and service quality parameters relative to service levels of requests, periodically determine a dispatch rate for requests of each service level, wherein the sum of the dispatch rate for respective service levels is less than or equal to a predetermined rate; and a request dispatcher configured to dispatch the requests of the corresponding service level in accordance with the dispatch rate determined by the rate controller. One aspect of the disclosure realizes a low overhead, highly scalable, simple and efficient workload management system to achieve QoS assurance and overload protection.