To adhere to the SOA model, WMProxy has been designed and implemented as a Simple Object Access Protocol (SOAP) Web service. The interface is described through the Web Service Description Language (WSDL). The WSDL file was written following the Web Services Interoperability Basic Profile (WS-I Basic Profile). This profile defines a set of Web Services specifications that promote interoperability.
The WMProxy service runs in an Apache container extended with Fast CGI and Grid Site modules.
- The Fast CGI module provides Common Gateway Interface (CGI) functionality with some other specific features. The most important advantage of Fast CGI is its performance and persistence. Fast CGI can be seen as a new implementation of CGI, designed to overcome CGI's performance problems. The major implementation differences are:
- Fast CGI processes are persistent: Fast CGI applications are able to serve multiple requests
- Application instances are spawned/killed dynamically according to demand
- Fast CGI protocol multiplexes the environment information, standard input, output, and error over a single full-duplex connection.
WMProxy is implemented as a single-threaded application thus ensuring more reliability and robustness than multi-threaded applications; thanks to the Fast CGI process manager the web server maintains a pool of processes that allow improving performances as generally done through multi-threaded application.
- Grid Site provides a module extending the Apache webserver for use within Grid frameworks by adding support for Grid security credentials such as Grid Security Infrastructure (GSI) and Virtual Organization Membership Service (VOMS), and file transfer over HTTPS. It also provides a library for handling Grid Access Control Lists (GACL).
The Web Service hosting framework provided by Apache, Grid Site and gSOAP has allowed the development of the WMProxy service using the C++ language. The choice of the implementation language has been driven mostly by the need to re-use and integrate existing production-quality components and libraries. A further boost in this direction has been given by preliminary tests that have shown better performance for the couple C++/gSOAP in comparison with the most commonly used framework for the development of Web Services (e.g., Axis/Java). Last but not least the gSOAP interoperability with a variety of other SOAP implementations and toolkits that permitted the development of a service accessible from clients written in different programming language and running on any computer platform.
Figure 1 - WMProxy Integration
The integration of the WMProxy within the WMS is shown in Figure 1. WMProxy provides a core module performing validation, conversion, environment preparation and information logging for each incoming request, before delivering it to the Workload Manager (WM). WM is the core component of the WMS taking the appropriate actions to satisfy incoming requests. Communication between the WMProxy and the WM occurs through a thread-safe, file-system based queue. The LBProxy, which is used as a state storage of active jobs, is the only external service with which the WMProxy interacts. The LBProxy service provides an optimized access to the Logging and Bookkeeping Service (LB). Other relevant information about processed jobs/requests are stored in the local file system in a reserved area managed by the WMS.
WMProxy is composed of different modules: WMProxy Modules
