As web-based transactions become an essential element of everyday corporate and commerce activities, it becomes increasingly important that the performance of web-based services be predictable and guaranteed even in the presence of wildly fluctuating input loads. In this paper, we propose a general implementation framework to provide quality of service (QoS) guarantee for cluster-based Internet services, such as E-commerce or directory service. We describe the design, implementation, and evaluation of a web request distribution system called Gage, which can provide every subscriber with distinct guarantee on the number of generic web requests that are serviced per second regardless of the total input loads at run time. Gage is one of the first systems that can support QoS guarantee involving multiple system resources, i.e., CPU, disk, and network. The front-end request distribution server of Gage distributes incoming requests among a cluster of back-end web server nodes so as to maintain per-subscriber QoS guarantee and load balance among the back-end servers. Each back-end web server node includes a Gage module, which performs distributed TCP splicing and detailed resource usage accounting. Performance evaluation of the fully operational Gage prototype demonstrates that the proposed architecture can indeed provide the guaranteed request throughput for different classes of web accesses, even in the presence of excessive input loads. The additional performance overhead associated with QoS support in Gage is merely 3.06%.