Advanced Resource Connector

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Advanced Resource Connector, or ARC, is a Grid middleware developed by NorduGrid. ARC is an open source software distributed under the GPL license. It enables production quality computational and data Grids.

Contents

[edit] Background

Early releases of ARC were known as the NorduGrid middleware. The first release was announced in May 2002. Since then, this middleware was installed and used in a variety of production Grid environments. Emphasis is put on scalability, stability, reliability and performance of the middleware. Resources inter-connected by the means of ARC constitute one of the largest production Grids in the world.

[edit] Middleware description

ARC provides a reliable implementation of the fundamental Grid services, such as information services, resource discovery and monitoring, job submission and management, brokering and data management and resource management. Most of these services are provided through the security layer of the Grid Security Infrastructure. The middleware builds upon standard Open Source solutions like the OpenLDAP, OpenSSL, SASL and Globus Toolkit (GT) libraries. All the external software is provided in the download area and the complete list of external software dependencies can be found here. NorduGrid provides innovative solutions essential for a production quality middleware: the Grid Manager, gridftpd (the ARC/NorduGrid GridFTP server), the information model and providers (NorduGrid schema), User Interface and broker (a "personal" broker integrated into the user interface), extended Resource Specification Language (xRSL), and the monitoring system.

The listed solutions are used as replacements and extensions of the original pre-WS services of the Globus Toolkit. ARC does not use most of GT services, such as GRAM, job submission commands, the WUftp-based gridftp server, the gatekeeper, GRAM job-manager scripts, MDS information providers or schemas. Moreover, ARC extends Globus RSL and makes the Globus MDS functional – without altering the original code. ARC is thus much more than a Globus Toolkit – it is an out-of-the-box Grid solution that offers its own services built upon the GT libraries.

The NorduGrid middleware integrates computing resources (usually, commodity computing clusters managed by a batch system or standalone workstations) and Storage Elements, making them available via a secure common Grid layer. An overview of the architecture can be found, e.g. in the NorduGrid architecture and tools presentation. Complete documentation, including component descriptions, installation details, usage instructions, articles and presentations, can be found at the NorduGrid Web site.

[edit] ARC main components

ARC components chart
Enlarge
ARC components chart

ARC basic components are:

  1. Grid services running on the resources: the Grid Manager, gridftpd and the information services. Grid jobs are submitted to a site through gridftpd and a separate session directory is created for each job. The Grid session directories are made available through the gridftpd server during and after job execution. The Grid Manager is a service running on a computing resource taking care of jobs, session directories and the input data cache area. Information services are implemented as efficient scripts populating the NorduGrid information database stored in the Globus-specific OpenLDAP backends.
  2. Indexing services for the resources and data: a special, simplified usage of the GT-2 GIIS OpenLDAP backend allows to build a hierarchical mesh of Grid-connected sites. For data indexing, ARC middleware can use a variety of services, such as the GT-2 Replica Catalog, the GT-2 RLS or gLite's Fireman. ARC client tools and the Grid Manager are capable of interacting with these services.
  3. Clients making intelligent use of the distributed information and data available on the Grid. ARC comes with a light-weight command line client, the User Interface. The ARC User Interface is a set of tools to submit, monitor and manage jobs on the Grid, move data around and query resource information. The User Interface comes with a built-in broker, which is able to select the best matching resource for a job. Grid job requirements are expressed via xRSL. Another special client is the Grid Monitor, which uses any Web browser as an agent to periodically query the distributed information system and present the results as a set of inter-linked Web pages.

Other important components are:

  1. Smart Storage Element (SSE): SSE is a replacement of the current ARC gridftpd-based simple storage element. SSE is based on standard protocols such as HTTPS/G and SOAP. SSE will provide flexible access control, data integrity between resources and support for autonomous and reliable data replication.
  2. Logging service.

ARC is designed to be a scalable, non-intrusive and portable solution. The development is user- and application-driven, with the main requirements being those of performance, stability, usability and portability. As a result of this approach, the standalone client is available for a dozen of platforms and can be installed in a few minutes. The server installation does not require a full site reconfiguration. The middleware can be built on any platform where the external software packages (like GT libraries) are available. While being deployed on a large production Grid and being used by real users, the middleware is naturally undergoing continuous real life tests.

[edit] ARC middleware availability

ARC middleware is free to be used anywhere by anybody. It is available from the NorduGrid public repository in pre-built binary distributions for a variety of Linux systems. Source code is also available from this repository and from the NorduGrid CVS.

Furthermore, a standalone client binary tarballs are available for a variety of Linux systems. This client comes with all the required external software (most notably, parts of the Globus Toolkit) and configuration, thus providing a complete, out-of-the-box client package that can be used by other Grids, e.g., for data transfer or data indexing.

Software releases are available under the GNU General Public License (GPL).

[edit] Development

The open source development of ARC middleware is coordinated by the NorduGrid collaboration. Contributions to the software, documentation and dissemination activities are coming from the community and from various projects, such as the EU KnowARC project, Nordic DataGrid Facility and various national Grid projects.

[edit] User support

ARC user support and installation assistance is provided by the NorduGrid via the request tracking system and a variety of mailing lists. Extensive documentation and tutorial materials are available at the NorduGrid Web site.

[edit] External links

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