The Grid is realizing the vision of providing computation as utility: computation jobs can be scheduled on-demand in Grid hosts based on available computation capacity. In this paper, we study another emerging usage of Grid utility: the hosting of application services. Different from a computation job, an application service such as e-Laboratory or on-line shopping has longer lifetime, and performs multiple jobs requested by its clients. A service Hosting Utility Platform (HUP) is formed by a set of servers in the Grid, and multiple application services will be hosted on the HUP.

We present the design and implementation of SODA, a Service-On-Demand Architecture that enables on-demand creation of application services on a HUP. With SODA, an application service will be created in the form of a set of virtual service nodes; each node is a virtual machine which is physically a ?slice? of a real host in the HUP. SODA involves both OS and middleware level techniques, and has the following salient capabilities: (1) on-demand service priming: the image of an application service as well as the OS on which it runs will be created on-demand and bootstrapped automatically; (2) better service isolation: services sharing the same HUP host are isolated with respect to administration, faults, attacks, and resources; (3) integrated service request management: for each service, a service switch will be created to direct client requests to appropriate virtual service nodes. Moreover, the application service provider can replace the default request switching policy with a service-speci.c policy.