An index based load balancer to enhance transactional application servers' QoS

The Web is the preferred interface for the new generation of applications. Web services are an ubiquitous concept for both, developers and managers. These Web applications require distribution systems of web requests that allow and support the dynamism of these environments, to provide service availability and resource usage, commonly heterogeneous. Web services provide an entry point to the Web application business logic. Therefore, the design of appropriate load balancing strategies, taking into account the dynamic nature of the application servers' activity, is essential. In this work we present a load balancing policy and its integration inbetween static and dynamic layers of any web application that uses application servers. The strategy gets the status report of each application server, used to later distribute web requests. Results that show how the strategy succeed are presented

Distribution pattern-driven development of service architectures

Distributed systems are being constructed by composing a number of discrete components. This practice is particularly prevalent within the Web service domain in the form of service process orchestration and choreography. Often, enterprise systems are built from many existing discrete applications such as legacy applications exposed using Web service interfaces. There are a number of architectural configurations or distribution patterns, which express how a composed system is to be deployed in a distributed environment. However, the amount of code required to realise these distribution patterns is considerable. In this paper, we propose a distribution pattern-driven approach to service composition and architecting. We develop, based on a catalog of patterns, a UML-compliant framework, which takes existing Web service interfaces as its input and generates executable Web service compositions based on a distribution pattern chosen by the software architect

Byzantine Fault-Tolerant Web Services for n-Tier and Service Oriented Architectures

Web Services that provide mission-critical functionality must be replicated to guarantee correct execution and high availability in spite of arbitrary (Byzantine) faults. Existing approaches for Byzantine fault-tolerant execution of Web Services are inadequate to guarantee correct execution due to several major limitations. Some approaches do not support interoperability between replicated Web Services. Other approaches do not provide fault isolation guarantees that are strong enough to prevent cascading failures across organizational and application boundaries. Moreover, existing approaches place impractical limitations on application development by not supporting long-running active threads of computation, fully asynchronous communication, and access to host specific information. We present Perpetual-WS, middleware that supports interaction between replicated Web Services while providing strict fault isolation guarantees. Perpetual-WS supports both synchronous and asynchronous message passing and enables an application model that supports long-running active threads of computation. We present an implementation based on Axis2 and performance evaluations demonstrating only a moderate decrease in throughput due to replication

Design and Implementation of a Byzantine Fault Tolerance Framework for Web Services

Many Web services are expected to run with high degree of security and dependability. To achieve this goal, it is essential to use a Web services compatible framework that tolerates not only crash faults, but Byzantine faults as well, due to the untrusted communication environment in which the Web services operate. In this paper, we describe the design and implementation of such a framework, called BFT-WS. BFT-WS is designed to operate on top of the standard SOAP messaging framework for maximum interoperability. It is implemented as a pluggable module within the Axis2 architecture, as such, it requires minimum changes to the Web applications. The core fault tolerance mechanisms used in BFT-WS are based on the well-known Castro and Liskov’s BFT algorithm for optimal efficiency. Our performance measurements confirm that BFT-WS incurs only moderate runtime overhead considering the complexity of the mechanisms

Dependable IPTV Hosting

This research focuses on the challenges of hosting 3rd party RESTful applications that have to meet specific dependability standards. To provide a proof of concept I have implemented an architecture and framework for the use case of internet protocol television. Delivering TV services via internet protocols over high-speed connections is commonly referred to as IPTV (internet protocol television). Similar to the app-stores of smartphones, IPTV platforms enable the emergence of IPTV services in which 3rd party developers provide services to consumer that add value to the IPTV experience. A key issue in the IPTV ecosystem is that currently telecommunications IPTV providers do not have a system that allows 3rd party developers to create applications that meet their standards. The main challenges are that the 3rd party applications must be dependable, scalable and adhere to service level agreements. This research provides an architecture and framework to overcome these challenges

FUSE: Lightweight Guaranteed Distributed Failure Notification

FUSE is a lightweight failure notification service for building distributed systems. Distributed systems built with FUSE are guaranteed that failure notifications never fail. Whenever a failure notification is triggered, all live members of the FUSE group will hear a notification within a bounded period of time, irrespective of node or communication failures. In contrast to previous work on failure detection, the responsibility for deciding that afailure has occurred is shared between the FUSE service and the distributed application. This allows applications to implement their own definitions of failure. Our experience building a scalable distributed event delivery system on an overlay network has convinced us of the usefulness of this service. Our results demonstrate that the network costs of each FUSE group can be small; in particular, our overlay network implementation requires no additional liveness-verifying ping traffic beyond that already needed to maintain the overlay, making the steady state network load independent of the number of active FUSE groups

Investigations into the model driven design of distribution patterns for web service compositions

Increasingly, distributed systems are being used to provide enterprise level solutions with high scalability and fault tolerance These solutins are often built using Web servces that are composed to perform useful business functions Acceptance of these composed systems is often constrained by a number of non-functional properties of the system such as availability, scalability and performance There are a number of drstribution patterns that each exhibit different non-functional charactmstics These patterns are re-occuring distribution schemes that express how a system is to be assembled and subsequently deployed. Traditional approaches to development of Web service compositions exhibit a number of Issues Firstly, Web service composition development is often ad-hoc and requires considerable low level coding effort for realisatlon Such systems often exhibit fixed architectures, making maintenance difficult and error prone Additionally, a number of the non-funchonal reqwements cannot be easily assessed by exammng low level code. In this thesis we explicitly model the compositional aspects of Web service compositions usmg UML Activity diagrams Ths approach uses a modehng and transformation framework, based on Model Dnven Software Development (MDSD), going from high level models to an executable system The framework is guided by a methodological framework whose primary artifact is a distribution pattern model, chosen from the supplied catalog. Our modelling and transfomation framework improves the development process of Web service compositions, with respect to a number of criteria, when compared to the traditional handcrafted approach Specifically, we negate the coding effort traditionally associated with Web service composition development Maintenance overheads of the solution are also slgnificantly reduced, while improved mutability 1s achieved through a flexible architecture when compared with existing tools We also improve the product output from the development process by exposing the non-functional runtime properties of Web service compositlons using distribution patterns