105,067 research outputs found
Towards Adaptable and Adaptive Policy-Free Middleware
We believe that to fully support adaptive distributed applications,
middleware must itself be adaptable, adaptive and policy-free. In this paper we
present a new language-independent adaptable and adaptive policy framework
suitable for integration in a wide variety of middleware systems. This
framework facilitates the construction of adaptive distributed applications.
The framework addresses adaptability through its ability to represent a wide
range of specific middleware policies. Adaptiveness is supported by a rich
contextual model, through which an application programmer may control precisely
how policies should be selected for any particular interaction with the
middleware. A contextual pattern mechanism facilitates the succinct expression
of both coarse- and fine-grain policy contexts. Policies may be specified and
altered dynamically, and may themselves take account of dynamic conditions. The
framework contains no hard-wired policies; instead, all policies can be
configured.Comment: Submitted to Dependable and Adaptive Distributed Systems Track, ACM
SAC 200
Platform-independent Dynamic Reconfiguration of Distributed Applications
The aim of dynamic reconfiguration is to allow a system to evolve incrementally from one configuration to another at run-time, without restarting it or taking it offline. In recent years, support for transparent dynamic reconfiguration has been added to middleware platforms, shifting the complexity required to enable dynamic reconfiguration to the supporting infrastructure. These approaches to dynamic reconfiguration are mostly platform-specific and depend on particular implementation approaches suitable for particular platforms. In this paper, we propose an approach to dynamic reconfiguration of distributed applications that is suitable for application implemented on top of different platforms. This approach supports a platform-independent view of an application that profits from reconfiguration transparency. In this view, requirements on the ability to reconfigure components are expressed in an abstract manner. These requirements are then satisfied by platform-specific realizations
Split and Migrate: Resource-Driven Placement and Discovery of Microservices at the Edge
Microservices architectures combine the use of fine-grained and independently-scalable services with lightweight communication protocols, such as REST calls over HTTP. Microservices bring flexibility to the development and deployment of application back-ends in the cloud.
Applications such as collaborative editing tools require frequent interactions between the front-end running on users\u27 machines and a back-end formed of multiple microservices. User-perceived latencies depend on their connection to microservices, but also on the interaction patterns between these services and their databases. Placing services at the edge of the network, closer to the users, is necessary to reduce user-perceived latencies. It is however difficult to decide on the placement of complete stateful microservices at one specific core or edge location without trading between a latency reduction for some users and a latency increase for the others.
We present how to dynamically deploy microservices on a combination of core and edge resources to systematically reduce user-perceived latencies. Our approach enables the split of stateful microservices, and the placement of the resulting splits on appropriate core and edge sites. Koala, a decentralized and resource-driven service discovery middleware, enables REST calls to reach and use the appropriate split, with only minimal changes to a legacy microservices application. Locality awareness using network coordinates further enables to automatically migrate services split and follow the location of the users. We confirm the effectiveness of our approach with a full prototype and an application to ShareLatex, a microservices-based collaborative editing application
An Infrastructure for the Dynamic Distribution of Web Applications and Services
This paper presents the design and implementation of an infrastructure that enables any Web application, regardless of its current state, to be stopped and uninstalled from a particular server, transferred to a new server, then installed, loaded, and resumed, with all these events occurring "on the fly" and totally transparent to clients. Such functionalities allow entire applications to fluidly move from server to server, reducing the overhead required to administer the system, and increasing its performance in a number of ways: (1) Dynamic replication of new instances of applications to several servers to raise throughput for scalability purposes, (2) Moving applications to servers to achieve load balancing or other resource management goals, (3) Caching entire applications on servers located closer to clients.National Science Foundation (9986397
Digital Preservation Services : State of the Art Analysis
Research report funded by the DC-NET project.An overview of the state of the art in service provision for digital preservation and curation. Its focus is on the areas where bridging the gaps is needed between e-Infrastructures and efficient and forward-looking digital preservation services. Based on a desktop study and a rapid analysis of some 190 currently available tools and services for digital preservation, the deliverable provides a high-level view on the range of instruments currently on offer to support various functions within a preservation system.European Commission, FP7peer-reviewe
Evolutionary paths to and from the red sequence: Star formation and HI properties of transition galaxies at z~0
(Abridged) We investigate the properties of galaxies between the blue and the
red sequence (i.e., the transition region) by combining UV and NIR imaging to
HI line observations for a volume-limited sample of nearby galaxies. We confirm
the existence of a tight relation between colour and HI-fraction across all the
range of colours, although outside the blue cloud this trend becomes gradually
weaker. Transition galaxies are divided into two different families, according
to their atomic hydrogen content. HI-deficient galaxies are the majority of
transition galaxies in our sample. They are found in high density environments
and all their properties are consistent with a quenching of the star formation
via gas stripping. However, while the migration from the blue cloud is
relatively quick (i.e., <=1 Gyr), a longer amount of time (a few Gyr at least)
seems required to completely suppress the star formation and reach the red
sequence. At all masses, migrating HI-deficient galaxies are mainly disks,
implying that the mechanism responsible for today's migration in clusters
cannot have played a significant role in the creation of the red sequence at
high-redshift. Conversely, HI-normal transition galaxies are a more
heterogeneous population. A fraction of these objects show evidence for
accretion/minor-merging events suggesting that at least part of the HI
reservoir has an external origin. The detailed evolution of such systems is
still unclear, but our analysis suggests that some galaxies might have migrated
back from the red sequence after accretion events. Our study clearly shows the
variety of evolutionary paths leading to the transition region and suggests
that the transition galaxies may not be always associated with systems quickly
migrating from the blue to the red sequence.Comment: 19 pages, 11 Figures, 1 Table. MNRAS in press. High resolution
version available at
http://www.astro.cardiff.ac.uk/pub/Luca.Cortese/papers/mnras09_1159_hires.p
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