Provendo segurança e uma semântica de falhas consistente para a comunicação de objetos assíncronos distribuídos.

Abstract

The development of distributed systems is a very complex activity, but it can be aided by appropriate middleware platforms. This work encompasses the niche of peer-to-peer distributed systems developed in Java, whose nodes need to maintain several connections opened simultaneously, because, as far as we concern, there is no middleware which supports all the demands of this niche. In order to evaluate that gap, we have elicited seven non-functional requirements for systems in the work niche: crash failure detection, message loss failure detection, concurrence, programming easiness, security, partial connectivity support and integration with the Java programming language. None of the five middleware that we evaluated met all the non-functional requirements, so we were motivated to develop a new middleware, called Commune, which would meet all these requirements. As a result, the Commune middleware could aid the development of systems in the niche of this work. In comparison with the evaluated middleware, Commune has two main contributions. Firstly, we carried out a bibliographic research in the extent of security for distributed systems, in order to implement security for Commune. We have created two mechanisms based on asymmetric key pair authentication and X.509 certification. In second place, we have defined the requirements for a comprehensive failure detection semantic, able to detect node crash failures and omission failures due to message lost in the communication channel. We have modelled a connection protocol for Commune, using a state machine to illustrate the state of Commune nodes, and we have proven that the proposed model meet all the requirements of the comprehensive failure detection semantic. It was necessary to use formal verification techniques, in order to prove that the connection protocol does not contain deadlocks. Moreover,we have shown the Commune architecture and implementation details. At last, we have evaluated the Commune performance, which is feasible when it is compared to Java RMI, and we have executed test in a production environment, with successful results.