wiki:InfoProvider
Last modified 9 years ago Last modified on 11/18/09 12:16:26

The dCache Info Provider

The dCache Info Provider is a dCache Component that runs independently of dCache and provides a description of a dCache instance using the GLUE information model?. It takes its information from the info service.

Overview

A description of a dCache instance is available via the info service. This description is dCache-specific, so only understood by tools and utilities that are tied to dCache or have some dCache-specific knowledge.

Within the Grid, it is desirable to decouple tools from specific implementations of a storage service; for example, tools that wish to undertake service discovery need some generic way to identify available storage, independent of whether sites are running dCache or some alternative storage software. For this reason, dCache can provide a description using a Grid-wide common language for describing grid components: GLUE.

The translation from dCache-specific output to GLUE description is achieved by the Info Provider. The Info Provider is presented as a small script, although the bulk of the work happens outside the script. Running this script will result in the LDIF (an LDAP file format) that describes the dCache instance being emitted on stdout.

Configuration

Some concepts within dCache are not easily converted to GLUE equivalents; likewise, GLUE contains some concepts that are alien to dCache.

An example of this is the SiteUniqueID; this is an ID that identifies a dCache instance as part of the collection of services that a site provides. A dCache instance has no knowledge of which site it is part of, so the info-provider must be configured so it knows this, and similar, information.

The configuration for the Info Provider is held in /opt/d-cache/etc/glue-1.3.xml. A template for this file is available: /opt/d-cache/etc/glue-1.3.xml.template. For most sites, simply copying the template file and updating the parameters at the beginning of the file is sufficient.

Deploying the info provider

The file /opt/d-cache/share/doc/README-GLUE provides a complete description of how to configure the Info Provider, how to verify it is working and suggested steps when diagnosing a problem. It is recommended that site admin reads this file and follows the procedures as described.

If a site is using dCacheconfigure.sh to maintain their configuration then much of the configuration and deployment process is automated. However, the process of configuring BDII must be completed manually. For information on how to achieve this, please read the "Configuring BDII" section of /opt/d-cache/share/doc/README-GLUE.

Testing a deployed info provider

The procedure for testing a deployed info provider is described in the file /opt/d-cache/share/doc/README-GLUE. This includes sample queries to verify that the information is propagating correctly. The document also includes information on how to diagnose faults.