R&D challenges and solutions for highly complex distributed systems: a middleware perspective

Highly complex distributed systems (HCDSs) are characterized by a large number of mission-critical, heterogeneous inter-dependent subsystems executing concurrently with diverse—often conflicting—quality-of-service (QoS) requirements. Creating, integrating, and assuring these properties in HCDSs is hard and expecting application developers to perform these activities without significant support is unrealistic. As a result, the computing and communication foundation for HCDSs is increasingly based on middleware. This article examines key R&D challenges that impede the ability of researchers and developers to manage HCDS software complexity. For each challenge that must be addressed to support HCDSs, the article surveys the state-of-the-art middleware solutions to these challenges and describes open issues and promising future research directions.