  Since its introduction, the Grid computing paradigm has been widely adopted
both in scientific and also in industrial areas. The main advantage of the Grid
computing paradigm is the ability to enable, in a transparent way, the sharing
and the coordination of several heterogeneous and large-scale distributed
resources belonging to different institutional domains. One of its limitation
is the lack of facilities for executing services. In fact, Grid computing has
been traditionally used and improved for running computational-intensive or
data-intensive applications. A service differs from this kind of applications
in that it usually waits for requests from clients and replies with useful
information; moreover, a service is typically subjected to some predefined
constraints, called Service Level Agreement (SLA), including both temporal and
performance restrictions. In this paper we present the TAAROA middleware, a
software system that tries to extend the traditional target of the Grid
computing paradigm to include the service concept. It attempts to accomplish
its goal by using the virtualization technology. By abstracting the hardware
and software resources of a computer, virtualization brings to TAAROA two
important benefits: (1) the encapsulation of the service runtime environment,
and (2) the possibility, through the migration facility, to move a service from
the computer where it is running to another one that hopefully reduces the risk
of violating some of the SLA constraints. In the current version of TAAROA
middleware there is no explicit mechanism for achieving the level of a service
as defined by the related SLA; this means that actually TAAROA is only able to
provide a best-effort service.
