Difference between revisions of "GCore Based Information System"

Revision as of 21:07, 30 March 2011

Information System

The gCube Information System (shortly, IS) plays a central role in a gCube Infrastructure: it delivers functionalities for the publishing, discovery and ‘real-time’ monitoring of the set of resources forming the infrastructure. It acts as the registry of the infrastructure, i.e. all the resources are registered in the IS and every service partaking to the infrastructure must refer to it to dynamically discover the rest of Infrastructure constituents. This is of great support for the dynamic deployment capabilities of gCube.

Resources can be:

• profile, statically characterising the resource, e.g. its type;
• instance state, characterising the operational state of an instance of a gCube service
• generic resource, any piece of well-formed information

Because of its central role, key requirements in terms of quality of service for such a subsystem are performance, scalability, freshness and availability. Moreover, facilities supporting the interaction with such subsystem have been included in the gCore Framework.

Reference Architecture

Figure 1 presents the components of the Information System and their main interactions. These can be classified as follows:

• production/publishing
• collection/storage
• consumption/query

Figure 1. Information System Architecture and Main Interactions

The components supporting the production/publishing phase are:

• IS-Registry – this Service supports the publishing/un-publishing of gCube resources; a gCube resource is advertised through its profile, i.e. the resource profile represents the existence of a resource;
• IS-gLiteBridge – this Service supports the publishing/un-publishing of resources gathered from a gLite based infrastructure; a gCube-based infrastructure include resources forming a gLite-based infrastructure;
• IS-Publisher – this Library supports services in publishing/un-publishing groups of resource properties as well as registering/un-registering groups of topics. Actually, this library is an interface other Services will rely on. Because of this fundamental role in supporting Services operation in a gCube-based infrastructure, a reference implementation of such an interface (gCubePublisher) is part of the gCore Framework;
• IS-Notification – this Library provides a Publish/Subcribe notification mechanism for Topics produced and consumed by services.

The component supporting the collection/storage phase is:

• IS-InformationCollector – this Service collects and makes available information related to the actual state of a gCube infrastructure and/or of an assigned subset of it;

The components supporting the consumption/query phase are:

• IS-Client – this Library supports Services in retrieving information published in the IS; it supports the discovery of both profiles and properties. Actually, this library is an interface Services will rely on. Because of this fundamental role in supporting Services operation in a gCube-based infrastructure, a reference implementation of such an interface (ExistLibrary) is part of the gCore Framework;
• IS-Notifier – this Service supports other Services in subscribing/unsubscribing to topics produced by the various Services; this service decouples the actual producer of the topic from the actual consumer allowing for producers re-location;
• IS-Manager – this Service supports other Services and clients in observing, checking, or keeping a continuous record of the status of the resources forming the infrastructure. Because of this role, it can also be classified as a component supporting the collection/storage phase but it is preferable to have it in the components supporting consumption/query phase because it is considered closer to this area. Since the IS-Manager is not yet an official component of the current IS subsystem and it is not delivered with it the documentation about the IS-Manager is not yet available.
• IS-Sweeper (coming soon) – this Executor plugin keep updated the GHN and RI profiles when the related GHN dies or have communication problems;

Design Notes

The IS has been conceived to rely on standards, most noticeable:

• WS-Notifications
• WS-ServiceGroup
• [htpp://docs.oasis-open.org/.../wsrf-ws_resource_properties-1.2-spec-os.pdf WS-ResourceProperty]
• Web Services Data Access and Integration – The XML Realization (WS-DAIX) Specification, Version 1.0
• XQuery 1.0

Early versions mostly exploited WS-ServiceGroup and WS-ResourceProperty specifications. Starting from version 2.0 (released in Feb 2011), the IS is designed around the WS-DAIX specification for publishing. WS-Notifications is at the heart of the functionalities delivered by the IS-Notifier service. Finally, the queries accepted by the IS has to be compliant with the XQuery language.

Worthy to mention, during the design of the IS, the following principle has been widely adopted: program to an interface, not an implementation. This means that we tried to maintain the IS consumers and producers as much as possible decoupled from its implementation. More concretely, a gCube service has to know only the IS-Client, IS-Notifier and IS-Publisher interfaces and that's all. It does not need to care about their implementation (mechanisms to dynamically load the IS-Client, IS-Notifier and IS-Publisher at runtime have been put in place) nor the actual IS deployment scenario (completely abstracted by the IS client libraries).