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In this paper, we present Harmony, a holistic messaging middleware for distributed, event-driven systems. Harmony supports various communication paradigms and heterogeneous networks. The key novelty of Harmony is the unified provision of endto- end quality of service, security, and resiliency, which shields the applications from the underlying network dynamics, failures, and security configurations. We describe the Harmony architecture in the context of cyber-physical business applications and elaborate on the design of its critical system components, including routing, security, and mobility support.
INTRODUCTION
Distributed event-driven applications have become increasingly popular in recent years, in part as a result of the proliferation of embedded computation and communication capabilities. Examples of these applications include energy and utility grids, intelligent transportation, telemedicine, industrial control, and inventory management. Until recently, most of these systems were deployed on a relatively small scale, typically using proprietary hardware and software components, such as special-purpose processors and operating systems. However, as the scope of these applications increases to cover a much larger number of nodes and they are distributed across larger geographic areas, a migration from mostly proprietary solutions to commoditized hardware, software, and networking technologies is desirable. While this migration will be aided by the pervasive deployment of wired and wireless networks, the commoditization of secure hardware components, and the maturing of virtualization technologies, it will only become feasible if the new infrastructures succeed in providing realtime performance, reliability, security, and privacy features on par with those associated with customized and proprietary solutions.
This paper presents Harmony, a novel messaging middleware for distributed, event-driven applications with stringent requirements for security, resiliency, and quality-of-service (QoS) parameters such as delay and throughput. It can operate on heterogeneous infrastructures using both wired and wireless networking technologies, and leverage the emerging capabilities in the area of trusted computing hardware.
To handle the mobility of and dynamic associations between endpoints, Harmony provides capabilities for autonomous organization of endpoints into domains based on their credentials, administrative ownership, application attributes, network connectivity, location, etc. Connectivity between these domains is controlled by security mechanisms that ensure delivery of encrypted messages to authorized endpoints only. The overlay is QoS-aware-i.e., it routes messages so as to achieve target levels of delay and throughput, and employs resilient multipath routing and message storage...