Distributed Information Service (DIS)
Overview
The DILIGENT Information Service (DIS) plays a central role in the gCube framework. The component does not have end-users; it supports the dynamic environment in place on any gCube infrastructure by maintaining and disseminating the picture of the infrastructure and its status at any time. This means that all the gCube resources are registered there and their status is continuously updated by the services in charge of managing them. Therefore, the information handled by the DIS includes:
- the profile of the all the gCube resources
- the status of the gCube service instances
The system exposes a uniform API to query its content and each service belonging to particular infrastructure can discover whatever is needed to the service to work properly.
One of its main exploitation is in the early stages of the dynamic Digital Library creation process. In fact, the Keeper and the Broker and MatchMaker services rely on the information exposed by the DIS to compile an optimal deployment plan for the new services of the rising DL.
The DIS architecture is designed on top of the Aggregator Framework software framework produced by the Globus Project and by exploiting the WS-ServiceGroup and WS-ResourceProperty specifications. The Aggregator Framework is a software framework that collects data from aggregator sources and sends data to aggregator sinks. It also allows implementing pluggable and customized sources and sinks and connecting them together following the WS-ServiceGroup specification. These capabilities have been exploited in the DIS by implementing some gCube services as aggregator sinks and allowing any gCube service to become an aggregator source. The data exchanged within the DIS connections are always and only WS-ResourceProperty documents. This allows the DIS to be as generic as possible and to be plugged with new aggregator sources at any time.
The DIS is also able to automatically harvest and expose information related to a gLite-based infrastructure. This result is achieved by interacting with the BDII Server, the gLite service playing the same role as the DIS in the context of the gLite infrastructure.
In this way, the gCube services that want to store data or run job to such a gLite infrastructure can obtain the needed information by using the same query API and without knowing the details of the BDII information schema.
Features
- built on top of the WS-ServiceGroup and WS-ResourceProperty specifications
- built on top of the Aggregator Framework
- allows gCube services to discover which resources are part of their Virtual Organization (VO)
- implements a uniform API to query arbitrarily structured resource information
- exposes WS-Topics about gCube changes about some pre-configured conditions
- allows to register arbitrary WS-Topics on any registered resource
- is open
- supports the runtime registration of new aggregator sources
- supports the construction of hierarchies of DIS
- gathers and exposes information (Computing Elements, Storage Elements, Sites) harvested from a BDII service of a gLite-based infrastructure
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Related Components & References
Collective Layer Service Group
Web Services Service Group 1.2 specification
Web Services Resource Property 1.2 specification