Building robust applications by reusing non-robust legacy software

Abstract

We propose a methodology for building robust Ada applications by reusing legacy software that we replicate among the nodes of a distributed system in order to increase fault tolerance of the service provided by the reused software. This methodology consists of writing an Ada interface which makes the binding to the legacy library. This interface forwards client requests to a group of remote servers, each one executing a copy of the legacy library. Dependability and consistency issues are solved inside the new interface code. In order to provide continuous service when adding new members, we propose techniques which prevent the server group from stopping service during state transfer. As an example of this methodology we present a robust database.