Conventional middleware systems fail to address important issues related to dynamism. Modern computer systems have to deal not only with heterogeneity in the underlying hardware and software platforms but also with highly dynamic environments. Mobile and distributed applications are greatly affected by dynamic changes of the environment characteristics such as security constraints and resource availability. Existing middleware is not prepared to react to these changes. In many cases, application developers know when adaptive changes in communication and security strategies would improve system performance. But often, they are not able to bene t from it because the middleware lacks the mechanisms to support monitoring (to detect when adaptation should take place) and on-the-y recon guration. dynamicTAO is a CORBA-compliant reective ORB that supports dynamic con guration. It maintains an explicit representation of its own internal structure and uses it to carry out runtime customizat...

We discuss the design and implementation of Egida, an objectoriented toolkit designed to support transparent rollback-recovery. Egida exports a simple specification language that can be used to express arbitrary rollback recovery protocols. From this specification, Egida automatically synthesizes an implementation of the specified protocol by gluing together the appropriate objects from an available library of “building blocks”. Egida is extensible and facilitates rapid implementation of rollback recovery protocols with minimal programming effort. We have integrated Egida with the MPICH implementation of the MPI standard. Existing MPI applications can take advantage of Egida without any modifications: fault-tolerance is achieved transparently—all that is needed is a simple re-link of the MPI application with Egida. 1

It is now well established that middleware platforms must accommodate an increasingly diverse range of requirements arising from the needs of both applications and underlying systems. Moreover, it is clear that to achieve this accommodation, platforms must be capable of both deployment-time configurability and run-time reconfigurability. This paper describes a middleware platform that addresses these requirements. The platform is built using a well-founded lightweight component model, uses reflective techniques to facilitate (re)configuration, and employs the notion of component frameworks to manage and constrain the scope of reconfiguration operations.

Modern computing environments face both low-frequency infrastructural changes, such as software and hardware upgrades, and frequent changes, such as fluctuations in the network bandwidth and CPU load. However, existing operating systems are not designed to cope with rapidly changing environments. They provide no mechanism to permit the insertion of self-adapting components that can optimize system performance according to diversity, software and hardware changes, and variations in the environment. They are not designed to accommodate dynamic updates of software, or to deal with component inter-dependence. This pa...

In a distributed object system such as Distributed Component Object Model (DCOM), legacy transport protocols used for communication limit the performance over high-speed networks. By making use of a lowlatency, high-bandwidth, and low overhead user-level networking architecture such as Virtual Interface (VI) Architecture, this performance bottleneck can be significantly reduced. Since user-level networking architectures provide low-level primitives, the challenge lies in integrating them into high-level applications. This requires a systematic approach. In this paper, a methodology to utilize VI Architecture to improve the performance of DCOM using custom object marshaling is developed. Initial experimental results demonstrate that the latencies of small messages in distributed object computing can be significantly reduced by this methodology.

Communication middleware systems provide a solid basis for the construction of distributed applications. Unfortunately they usually lack the mechanisms for runtime reconfiguration. The performance of distributed applications is greatly affected by dynamic changes on the characteristics of the environment such as memory, CPU, and network availability. Existing communication middleware does not react in front of these changes. Most of the times, applications have enough knowledge to decide what to do in front of an environmental change, but they cannot use that knowledge because the middleware does not allow on-the-fly reconfiguration. We developed dynamicTAO, a CORBA-compliant reflective ORB that supports runtime reconfiguration. dynamicTAO maintains an explicit representation of its own internal structure and uses it to carry out dynamic customization safely.

Recent advances in distributed, mobile, and ubiquitous systems are creating new computing environments that are characterized by a high degree of dynamism. Variations in resource availability, network connectivity, and hardware and software platforms impact greatly the performance of user applications. The expected growth of ubiquitous computing will further change the nature of the computational infrastructure, bringing a plethora of small devices and requiring customized protocols and policies in order to fulfill the user’s evolving quality of service requirements. In the past ten years, software developers witnessed the creation of various middleware technologies whose goal is to facilitate the development of software systems. Middleware resides between the operating system and the application (thus its name), mediating the interactions between them. Technologies such as OMG’s CORBA 3, Sun’s Java-based J2EE, and Microsoft’s.NET hide from the programmer the complicated details of network communication, remote method invocation, naming, and service instantiation, easing the construction of complex distributed systems.

Developing distributed applications is a difficult task due to three major problems: the complexity of programming interprocess communication, the need to support services across heterogeneous platforms, and the need to adapt to changing conditions. Traditional middleware

Communication middleware systems provide a solid basis for the construction of distributed applications. However, they usually lack the mechanisms for runtime reconfiguration of the middleware engine. The performance of distributed applications is greatly affected by dynamic changes on the characteristics of the environment such as memory, CPU, and network availability. Existing communication middleware do not react in front of these changes. Most of the times, applications have enough knowledge to decide what to do in front of an environmental change, but they cannot use that knowledge because the middleware does not allow on-the-fly reconfiguration. We have developed dynamicTAO, a CORBA-compliant reflective ORB that supports runtime reconfiguration. dynamicTAO maintains an explicit representation of its own internal structure and uses it to carry out dynamic customization safely. This report describes the problems encountered during the design and implementation of our architectural frame...

This dissertation examines how the architectural layering of middleware constrains the design of a middleware security architecture, and analyses the complications that arise from that. First, we define a precise notion of middleware that includes its architecture and features. Our definition is based on the Common Object Request Broker Architecture (CORBA), which is used throughout this dissertation both as a reference technology and as a basis for a proof of concept implementation. In several steps, we construct a security model that fits to the described middleware architecture. The model facilitates conceptual reasoning about security. The results of our analysis indicate that the cryptographic identities available on the lower layers of the security model are only of limited use for expressing fine-grained security policies, because they are separated from the application layer entities by the middleware layer. To express individual application layer entities in access policies, additional more fine-grained descriptors are required. To solve this problem for the target side (i.e., the receiving side of an invocation), we propose an improved middleware security model that supports individual access policies on a per-target basis. The model is based on so-called "resource descriptors", which are used in addition to cryptographic identities to describe application layer entities in access policies. To be useful, descriptors need to fulfil a number of properties, such as local uniqueness and persistency. Next, we examine the information available at the middleware layer for its usefulness as resource descriptors, in particular the interface name and the instance information inside the object reference. Unfortunately neither fulfils all required properties. However, it ...