Grid and Web services are both hot topics today. In this paper, we will present some ongoing work and planned future work at the Cambridge eScience Centre. After an introduction to these technologies in the context of Grid applications development, we describe two use-cases: a database
of results in computational fluid dynamics (CFD) and a small computational Grid for aircraft engineering design.
As Grid services are moving towards Web services, we continue
to make use of the Globus Toolkit v2.4 (GT2.4), without
adopting the Open Grid Services Architecture (OGSA)
wholesale. In our scenario, GT2.4 integrates distributed
computing resources including HPC and clusters while Web
services wrap the scientific code as a service.Proceedings of the IEEE International Conference on Services Computing, Shanghai, September 200

Hayes, M

Spivack, M

Usher, A

Yang, X

English

Apollo (Cambridge)

Developing Web Services in a Computational Grid EnvironmentXiaobo Yang, Mark Hayes, Andrew UsherCambridge eScience CentreUniversity of CambridgeWilberforce RoadCambridge CB3 0WA, UK{xy216, mah1002, acju2}@cam.ac.ukMark SpivackDepartment of Applied Mathematics and Theoretical PhysicsUniversity of CambridgeWilberforce RoadCambridge CB3 0WA, UKM.Spivack@damtp.cam.ac.ukAbstractGrid and Web services are both hot topics today. In thispaper, we will present some ongoing work and planned fu-ture work at the Cambridge eScience Centre. After an intro-duction to these technologies in the context of Grid applica-tions development, we describe two use-cases: a databaseof results in computational uid dynamics (CFD) and asmall computational Grid for aircraft engineering design.As Grid services are moving towards Web services, we con-tinue to make use of the Globus Toolkit v2.4 (GT2.4), with-out adopting the Open Grid Services Architecture (OGSA)wholesale. In our scenario, GT2.4 integrates distributedcomputing resources including HPC and clusters while Webservices wrap the scientic code as a service.1. IntroductionGrid and Web services are currently attracting intenseinterest. As Web services mature towards an industry stan-dard, they have received a great deal of attention from theGrid computing community. Extensions of Web serviceshave been developed as Grid services, which are defined inthe Open Grid Services Infrastructure (OGSI) [14] speci-fications. Therefore, a Grid service is actually a Web ser-vice that conforms to a particular set of conventions besidesthose for Web services. For example, both Grid services andWeb services are defined in terms of standard WSDL (WebServices Definition Language) and make use of standardWeb service binding technologies such as SOAP (SimpleObject Access Protocol). But Grid services conventions arebeyond these and attempt to address problems such as thestate of services with lifetime management. The relation-ship between Grid services and Web services is given indetail by Grimshaw and Tuecke [11].The Open Grid Services Architecture (OGSA) attemptsto define a set of high level Grid services for batch job man-agement, monitoring, database access etc. OGSI was in-tended to provide a conceptual foundation for building thesehigher level services which are used directly by Grid appli-cations. One can illustrate this framework in a classic lay-ered stack diagram (see Fig. 1).ApplicationsOGSAOGSI/WS-RFWeb servicesCompute/Data resourcesFigure 1. OGSA stack.While the OGSI specifications provide a way to developGrids based on Web services standards, Foster noted threemajor concerns at the GlobusWORLD 2004 conference:OGSI places “too much stuff in one specification”, “doesnot work well with existing Web services tooling” and is“too ‘object oriented’ ”. The new WS-Resource Frame-work (WS-RF) [1] proposed by the Globus Alliance, IBM,HP and others addresses these issues. Future implementa-tions of the Globus Toolkit will be based on WS-RF ratherthan OGSI. At the time of writing, the WS-RF specifica-tions have just entered the standards process at OASIS [2].Stable implementations may be some time in appearing.Therefore we chose to continue using the “mature” GT2.4in our test bed. In this paper, we will first describe some pre-liminary work on Web services, followed by our thoughtson developing secure Web services in a Grid environment.Our planned future work will be described with conclusionsgiven in the last section.2. Preliminary work on Web services develop-mentGrids [10] offer the possibility of aggregating the capa-bilities of geographically distributed computing resources.In today’s engineering and scientific research, numericalcomputational techniques are heavily utilised. Usuallythese techniques are in constant pursuit of ever larger com-puting resources in order to produce increasingly preciseand reasonable results. Also research work today com-monly involves large scale cooperation between many (in-ternational) institutes and universities. While the Grid aimsto share resources and set up virtual organisations (VOs),Web services help to realise this by exposing applications,databases and other resources as network-accessible com-ponents.One of the projects based at the Cambridge eScienceCentre [3] is the application of Grid-based technology tocombustion CFD [4]. With the computational Grid environ-ment setup successfully [12, 15], some meaningful compu-tational results are ready to be shared with the CFD com-munity. Therefore this project is selected as our prelimi-nary case study. First, we set up an XML database with de-scriptions of each dataset, or meta-data. Information suchas the creator of the dataset, the date the dataset is createdtogether with some physical parameters is included. Withthe database set up, we next want to make it visible to thepublic. Therefore we develop a Web service to visit thedatabase. We expose this service with Apache Axis [5] andprovide a client as a Java servlet. Now everyone is able toconsume our Web service though the servlet, i.e., he or shecan query the database to search for results of interest. TheWSDL file of the service is also published so that users areable to develop their own clients. The structure of the ser-vice is depicted in Fig. 2.SOAPWeb BrowserWeb ServerApache AxisXMLDatabaseHTTPFigure 2. Structure of the CFD query Web ser›vice.Part of a query result of the above CFD query Web ser-vice is show in Fig. 3. The query condition is set as querying“Peak wave number” with the condition “< 20.0” througha Web form shown in Fig. 2. A query statement is automat-ically constructed within the Java servlet, then submitted tothe CFD Query Web service. The query result is handled bythe Java servlet to generate a static HTML page using XSLTransformations (XSLT) [6] or simply return the query re-sult in XML format.Figure 3. One query result of the CFD queryWeb service.As we can see from Fig. 3, CFD datasets are given withdescriptions while the real data is returned as Web link. Thisis mainly due to the huge size of each dataset. It also makesit flexible to let dataset providers control how to publishtheir datasets. For example, they may publish their data ona Web server, a FTP server, etc. Of course security policiesmay be applied by each dataset provider. In order to helpdataset providers to publish their dataset descriptions (XMLfiles to be added to our database), we have developed an-other Web service. Obviously we do not want everyone towrite to our database. Therefore security policies must beconsidered for this service. With mature transport-level se-curity techniques (SSL/TLS over HTTP), we successfullytested basic HTTP authentication based on SSL. ApacheAxis provides a powerful function which enables develop-ers to develop their own handlers to deal with the incom-ing/outgoing SOAP messages. A handler has been devel-oped to allow only secure connections to our service. Fur-thermore, message-level security has also been tested. Inthis case, we tested XML signature [7] to sign the documentthe user wants to add to the database to keep its integrity.3. Developing secure Web services in a compu-tational Grid environmentIn a computational Grid environment, security is one ofthe first and most important factors considered as it ofteninvolves direct access to hardware, software or data on com-puting resources. Therefore when a service is deployed, itis necessary to apply some security policies to secure theservice. As described above, standard transport-level secu-rity techniques (SSL/TLS over HTTP) are natural choicesfor end-to-end security and authentication. In a computa-tional Grid environment, we also require authorisation poli-cies to use a specified resource and single sign-on (SSO) foraccess to multiple resources. The Globus GSI (Grid Secu-rity Infrastructure) [9] provides these features. An examplewill be given below to describe the problem we meet whendeveloping a Web service to make use of a computationalGrid.Suppose we want to wrap the job submission function ofGT2.4 as a Web service, a proxy is required when a job issubmitted to a GRAM (Globus Resource Allocation Man-ager). Basically we can provide such a proxy in two ways.1) The Web service asks its client to provide the user’spassphrase of his or her private certificate. Then a proxywill be created by the Web service itself.2) The Web service asks its client to provide a proxy asone of its input parameters. In this way the client must haveuser’s private certificate to generate such a proxy either byGT2.4 itself or MyProxy [13].In the first method, transmission of user’s passphrase ofhis/her private certificate and access to his/her private cer-tificate by the Web service is needed. While in the secondone, a user should keep his/her own private certificate withGlobus Toolkit client or MyProxy client installed. The sec-ond method is widely adopted by portal developers sincea user is better protected than the first way. Therefore wewould also select this method to develop our Web services.4. Future workEMGrid [8], one of the projects hosted at the CambridgeeScience Centre, is the context for our second case studyon developing secure Web services within a computationalGrid environment. This project aims to optimise the de-sign of shape and of material properties for aircraft by us-ing radar scattering. The numerical simulation code splitsnaturally into two separate parts. The first part, say, codeA, is used to provide raw data for further processing. Thesecond part, code B is used to process the raw data gener-ated by code A for visualisation. Code A, which is highlycomputationally intensive, usually runs on a backend highperformance computing facility (HPCF). Code B is suitablefor running on a normal Linux cluster.ClusterCluster frontendHPCFHPCF frontendClientSOAPSOAPSOAPFigure 4. Architecture of a Web service sys›tem.Figure 4 illustrates the architecture of such a Web ser-vices system. Two distinct backend hosts, a HPCF and acluster, are included. Each backend host has its own fron-tend to expose its service. As mentioned above, the HPCFfrontend contains the code A service (service A) while thecluster has code B service (service B). At the first stage, wehope to visit each service separately from a client. While atthe second stage, we hope to combine both services to pro-vide an integrated service for scientists or engineers to per-form real-time design with feedback corrections. Althoughhere we simply put a ”Client” in Fig. 4, the real client can beas simple as a client java code of service A or B. It can alsobe as complex as a portal Web server (Fig. 5). According toour experience in portal and portlet design [15], a Web por-tal server could be a good choice to provide a user friendlyinterface for end users to consume services A and B.Portal Web ServerPortlet APortlet DPortlet BPortlet CMyProxyServerService AService BMoreServicesHTTP(S)Web BrowserFigure 5. Complex client  portal Web serverstructure.5. ConclusionsIn this paper, we first give a description of our pre-liminary work developing Web services for Grid applica-tions where secure authentication and authorization are re-quired. Both transport-level security (HTTP+SSL/TLS) andmessage-level security (XML signature) have been testedsuccessfully as authentication mechanisms. We have alsoproposed an architecture using Web services in a computa-tional Grid environment, with Globus GSI as an authorisa-tion framework.References[1] http://www.globus.org/wsrf/.[2] http://www.oasis-open.org/.[3] http://www.escience.cam.ac.uk/.[4] http://www.escience.cam.ac.uk/projects/cfd/.[5] http://ws.apache.org/axis/.[6] http://www.w3.org/TR/xslt.[7] http://www.w3.org/TR/xmldsig-core/.[8] http://www.escience.cam.ac.uk/projects/emgrid/.[9] I. Foster, C. Kesselman, G. Tsudik, and S. Tuecke. A se-curity architecture for computational Grids. In Proc. 5thACM Conference on Computer and Communications Secu-rity Conference, pages 83–92, 1998.[10] I. Foster, C. Kesselman, and S. Tuecke. The anatomy of theGrid: Enabling scalable virtual organizations. InternationalJ. Supercomputer Applications, 15(3), 2001.[11] A. Grimshaw and S. Tuecke. Grid services extend Web ser-vices. Web Services Journal, 3(8):22–26, 2003.[12] K. Jenkins, X. Yang, M. Hayes, and S. Cant. Distributedcomputational fluid dynamics. In Proc. UK e-Science AllHands Meeting 2003, edt. S.J. Cox, pages 862–864, Not-tingham, UK, 2-4 September 2003.[13] J. Novotny, S. Tuecke, and V. Welch. An online credentialrepository for the Grid: MyProxy. In Proc. of the TenthInternational Symposium on High Performance DistributedComputing (HPDC-10), IEEE Press, 2001.[14] S. Tuecke, K. Czajkowski, I. Foster, J. Frey, S. Graham,C. Kesselman, T. Maguire, T. Sandholm, P. Vanderbilt, andD. Snelling. Open Grid Services Infrastructure (OGSI)Version 1.0. Global Grid Forum Draft Recommendation,6/27/2003.[15] X. Yang, M. Hayes, K. Jenkins, and S. Cant. The Cam-bridge CFD Grid portal for large-scale distributed CFD ap-plications. In International Conference on ComputationalScience 2004, eds. M. Bubak et al., Springer-Verlag, LNCS3036, pages 478–481, Krako´w, Poland, 6-9 June 2004.

A security architecture for computational Grids.

An online credential repository for the Grid: MyProxy.

Distributed computational uid dynamics.

Grid services extend Web services.

Open Grid Services Infrastructure (OGSI) Version 1.0. Global Grid Forum Draft Recommendation,

The anatomy of the Grid: Enabling scalable virtual organizations.

The Cambridge CFD Grid portal for large-scale distributed CFD applications.

Developing web services in a computational grid environment

Developing web services in a computational grid environment

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