Quality-constrained routing in publish/subscribe systems

Routing in publish/subscribe (pub/sub) features a communication model where messages are not given explicit destination addresses, but destinations are determined by matching the subscription declared by subscribers. For a dynamic computing environment with applications that have quality demands, this is not sufficient. Routing decision should, in such environments, not only depend on the subscription predicate, but should also take the quality-constraints of applications and characteristics of network paths into account. We identified three abstraction levels of these quality constraints: functional, middleware and network. The main contribution of the paper is the concept of the integration of these constraints into the pub/sub routing. This is done by extending the syntax of pub/sub system and applying four generic, proposed by us, guidelines. The added values of quality-constrained routing concept are: message delivery satisfying quality demands of applications, improvement of system scalability and more optimise use of the network resources. We discuss the use case that shows the practical value of our concept

Reconfiguration Service for Publish/Subscribe Middleware

Mission-critical, distributed systems are often designed as a set of distributed, components that interact using publish/subscribe middleware. Currently, in these systems, software components are usually statically allocated to the nodes to fulfil predictability, reliability requirements. However, a static allocation of components has major drawbacks, e.g. the need for quantification of the expenditure of resources to prevent a lack of resources during runtime. A dynamic allocation diminishes the drawbacks of a static allocation by reallocating components during system run-time. The process of dynamic reallocation is considered as a reconfiguration of the system, which can be implemented as an additional functionality of the middleware. In this paper, we propose a new dynamic reconfiguration service for a publish/subscribe middleware that enables dynamic reallocation of components in order to achieve predictable and reliable system behaviour and fulfil deployment requirements. We have built a prototype that validates our research

Preservation of correctness during system reconfiguration in Data Distribution Service for Real-Time Systems (DDS)

This paper addresses dynamic reconfiguration of distributed systems that use a publish/subscribe (pub/sub) middleware. The objective of dynamic reconfiguration is to evolve incrementally from one system configuration to another at run-time in order to e.g., ensure the reliability of the system. The correctness notion of a distributed system is introduced that assures that the system parts that interact with entities under reconfiguration do not fail because of reconfiguration. We analyse the OMG specification of pub/sub systems - DDS (Data Distribution Service for Real-Time Systems) with respect to its support for the correctness preservation during reconfiguration. We notice that the DDS specification defines such an architecture and behaviour of the pub/sub system that automatically preserves correctness. This differentiates the DDS from other middleware technologies that require that the correctness preservation is guaranteed on application level or by reconfiguration manager/controller. We give several examples of automatic correctness preservation supported by the DDS