The high expectations raised by grid computing have favored the development and deployment of a growing number of grid infrastructures and middlewares. However, the interaction between these grids is still limited, so reducing the potential large-scale application of grid technology, in spite of efforts made by grid community. In this sense, the Open Grid Forum (OGF) is developing open standards for grid software interoperability, while the OGF’s Grid Interoperation Now Community Group (GIN-CG) is coordinating a set of interoperation efforts among production grids. It is therefore clear that, according to OGF (as Laurence Field explains in his article entitled “Getting Grids to work together: interoperation is key to sharing”), there is a big difference between these two terms:
- Interoperability is the native ability of grids and grid technologies to interact directly via common open standards.
- Interoperation is a set of techniques to get production grid infrastructures to work together in the short term.
Since most common open standards to provide grid interoperability are still being defined and only a few have been consolidated, grid interoperation techniques, like adapters and gateways, are needed. An adapter is, according to different dictionaries of computer terms, “a device that allows one system to connect to and work with another”. On the other hand, a gateway is conceptually similar to an adapter, but it is implemented as an independent service, acting as a bridge between two systems. The main drawback of adapters is that grid middleware or tools must be modified to insert the adapters. Gateways can be accessed without changes on grid middleware or tools, but they can become a single point of failure or a scalability bottleneck.
GridWay provides support for some of the few established standards like DRMAA, JSDL or WSRF to achieve interoperability but, in the meanwhile, it also provides components to allow interoperation, like Middleware Access Drivers (MADs) acting as adapters for different grid services, and the GridGateWay, which is a WSRF GRAM service encapsulating an instance of GridWay, thus providing a gateway for resource management services.
GridWay 4.0.2, coinciding with the release of Globus Toolkit 4 and its new WS GRAM service, introduced an architecture for the execution manager module based on a MAD (Middleware Access Driver) to interface several grid execution services, like pre-WS GRAM and WS GRAM, even simultaneously. That architecture was presented in the paper entitled “A modular meta-scheduling architecture for interfacing with pre-WS and WS Grid resource management services” (E. Huedo, R. S. Montero and I. M. Llorente). GridWay 5.0 took advantage of this modular architecture to implement an information manager module with a MAD to interface several grid information services, and a transfer manager module with a MAD to interface several grid data services. Moreover, the scheduling process was decoupled from the dispatch manager through the use of an external and selectable scheduler module.
The resulting architecture, which is shown above, provides direct interoperation between different middleware stacks. In fact, we demonstrated at OGF22 the interoperation of three important grid infrastructures, namely EGEE (gLite-based), TeraGrid and OSG (both Globus-based), being coordinately used through a single GridWay instance by means of the appropriate adapters. To set an example, the application was written using the DRMAA OGF standard. GridWay documentation provides a lot of information on how to integrate GridWay in the main middleware stacks, like gLite, pre-WS and WS Globus, or ARC, and provides information on how to develop new drivers for other middlewares.
Regarding the GridGateWay, it is being used for provisioning resources from several infrastructures. For example, the German Astronomy Community Grid (GACG or AstroGrid-D) uses a GridGateWay as a central resource broker, providing metascheduling functionality to Globus-based submission tools (e.g. for workflow execution) without modification. GridAustralia also uses a GridGateWay as a WSRF interface for its central GridWay Metascheduler instance, allowing reliable, remote job submission.
Picture by AstroGrid-D
More information about the GridGateWay component is provided in its web page, as well as in this blog entry, which shows how to build Utility Computing infrastructures with this Globus-based gateway technology.