Abstract: Middleware configurations provide a means to make accessible a wide range of applications on a (possibly large) distributed heterogeneous platform. However, as new application areas appear, middleware configurations will have to evolve to accommodate those new applications' needs. This paper discusses the implementation of the Aster development environment that realizes automatic configuration of middleware which are customized to the applications' needs from the standpoint of provided non-functional properties (e.g., fault-tolerance, security). The environment relies on two main tools. The first tool retrieves the software constituting the middleware that meets application requirements, by means of software specification matching. The second tool implements the interfacing of the application's software components with the customized middleware. Interfacing is discussed in the framework of the CORBA environment, hence addressing construction of customized middleware on top of an ORB, possibly using common object services specified by the OMG.