gLite is a stack of generic middleware on EGEE infrastructure.

Introductory documentation about gLite components can be found here:

• gLite-3-UserGuide

• Release independent documentation

gLite components cover a wide range of functionalities and applications. Below you can find a short description of main gLite compoments with links to official web page for each of them:

• User Interface
  
  • gLiteUI is the user access point to the EGEE infrastructure. Access to resources in EGEE infrastructure is based on digital personal certificates released to each user by a recognized CA (Certification Authority). Given a valid user certificate, gLiteUI provides the user with a command interface to other gLite components in order to carry out job management resource status information retrieval.
• Security:
  • VOMS, the Virtual Organization Management Service, is used in EGEE to manage information and privileges of users within a VO. Provided a user's personal certificate, on request, it generates short lasting proxy certificates allowing the user to access available EGEE resources.

• Information Service in gLite involves a series of modules spread across several components which all together provide a source of information about the EGEE Grid resources and their status. On the base of collected information resource discovery, monitoring and accounting activities are carried out. Much of the information published to the IS conforms to the GLUE schema, which defines a common conceptual data model to be used for Grid resource monitoring and discovery.

  • Information is published by the gLite services to a BDII (Berkeley Database Information Index) service which is used to store data both at a single site level and a top level, collecting information from multiple sites.

• Job Management:
  • gLiteWMS Workload Management System is the gLite component responsible for distributing and managing tasks across computing and storage resources available on several Grid infrastructures ( EGEE, NAREGI, OSG, Nordugrid). WMS assigns user jobs to available CEs and SEs resurces matching user job requirements specified trhough a series of Job Description Language (JDL) statements. WMS also provides failure recovery features such as authomatic resubmission.
  • gLiteLB is the Logging and Bookkeeping utility coupled to the gLiteWMS service. It keeps fresh information about the status of jobs processed by associated gLiteWMS instances allowing user for jobs status checks.
• Computing services: these include a Computing Element acting as a Grid interface to a cluster of computing resources localized at a site (cluster, farm...), a LRMS (Local Resource Management System) also known as batch system and the cluster itself, a collection of Worker Nodes (WNs), the nodes where the jobs are run.
  • lcgCE is the current CE service implementation of the production infrastructure, based on Globus toolkit. It can be configured for both Torque and LSF batch systems and both direct submission and via WMS submission is implemented.
    
  • CREAM CE (Computing Resource Execution And Management) service is a simple, lightweight service for job management operation at the Computing Element (CE) level. Both direct submission and via WMS submission is implemented (WMSICE component). Local Resource Manager (LRMS) is implemented via BLAH. All the resource management systems supported by BLAH are automatically supported by CREAM.
  • gLiteWN is the service implementing the Working Node, where user jobs actually run. It receives jobs by the local batch system of considered site.
    
• Data Management:
  

  • Storage Element provides uniform access to data storage resources. The Storage Element may control simple disk servers, large disk arrays or tape-based Mass Storage Systems (MSS). Most WLCG/EGEE sites provide at least one SE. Most storage resources are managed by a Storage Resource Manager (SRM) which has several implementation like DPM or dcache.

  • LFC Files in the Grid can be referred to by different names: Grid Unique IDentifier (GUID), Logical File Name (LFN), Storage URL (SURL) and Transport URL (TURL). While the GUIDs and LFNs identify a file irrespective of its location, the SURLs and TURLs contain information about where a physical replica is located, and how it can be accessed. In order to locate a file in the Grid, a user will normally use an LFN. LFNs are usually more intuitive, human-readable strings, since they are allocated by the user. The mappings between LFNs, GUIDs and SURLs are kept in a service called a File Catalogue, implemented in gLite as LCG File Catalogue (LFC),

  • FTS The File Transfer Service (FTS) is the gLite 3.1 low level data movement service. The user can schedule asynchronous and reliable file replication from source to destination (point-to-point, i.e. no file routing via intermediate storage) while participant sites can control the network usage. The FTS handles internally the SRM negotiation between the source and destination SEs and the management of the underlying GridFTP transfers.

• Monitoring:

  • RGMA R-GMA is an implementation of the Grid Monitoring Architecture (GMA) proposed by the Global Grid Forum (GGF). R-GMA is currently used for accounting and both system- and user-level monitoring. It also holds the same GLUE schema information as the MDS; this is not currently used to locate resources for job submission, though

  • FTM is a File Transfer Monitor performing queries to the gliteFTS component and publishing information both through summary files and a web page with hourly, daily and weekly intervals.