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Grid Middleware

The idea of distributed computing has been around for years. What distinguishes Grid computing from typical distributed computing or cluster computing is that grids tend to be more loosely coupled, heterogeneous, and geographically dispersed. Also, while a computing grid may be dedicated to a specialized application, it is often constructed with the aid of general purpose grid software libraries and middleware. Grid Middleware allows to submit requests to execute a computation (called a Job) to the Grid, s.t. it can be run anywhere in the network. Other software components such as “resource broker”, “replica manager” and others complement the middleware and distribute the job to the node that seems to be the best suitable for this job.

For the user of the middleware these details are hidden, for the user only the outcome is relevant: The job is executed somewhere else. Grid middleware can be seen as Operating System of the virtual Super Computer that in reality consists of many independent nodes on different sites, but appears to the user as one computational unit.

A very important aspect of Grid Middleware is Security. What a user can do depends on his authorisation, which is determined by his membership in so called “Virtual Organisations”. Authorisation is done most of the times via a standard certificate infrastructure.

Another aspect that needs to be handled by Grid Middleware is the following: Each institution has control over its domain, each institution may have different systems and policies. Grid Middleware is used to overcome this heterogeneity and to provide an interface at the boundary of this administrative domain. Figuratively we can describe the problem as an "hour glass": At one end there is a diverse set of resources and at the other end there are many virtual organizations that have their own applications. The applications can gain access to the heterogeneous resources through a small set of well defined interfaces – the Grid Middleware.

There are several middleware solutions around. Some of the most popular are listed below.

Grid Middleware List

This document from the OMII-Europe project contains a comparison of various Grid middleware. This can be useful when deciding which middleware is best suited to a given application.