www.neresc.ac.uk experiences with converting my grid web services to grid services savas...
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Experiences with Converting myGrid Web Services to Grid Services
Experiences with Converting myGrid Web Services to Grid Services
Savas Parastatidis & Paul WatsonSavas Parastatidis & Paul Watson
http://www.neresc.ac.uk/projects/CGM/web
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Overview
• Motivation• Building Grid Applications• Plans/Deliverables• myGrid Workflow Enactment Service• myGrid Notification• Conclusions
• More informationhttp://www.neresc.ac.uk/projects/CGM/web
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Motivation/Context for this work :-)
• The centre is involved in a number of Grid-related research projects• GOLD, OGSA-DAI, Polar*, BASIS, GridMIST, GridSHED, exSys, e-
Demand, myGrid, Microbase, Neuroinformatics
• Issues identified• Commonalities in software requirements• Possibilities of reusing software components• Testing• User education/tutorials
• Experience required in transforming existing Web Services to Grid Services
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Building Grid Applications
• Current approach by many UK e-Science projects
• The OGSA approach
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The NEReSC Core Grid Middleware
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Plans/Deliverables
• Quality control• Packaging• User documentation• Tutorial material• Courses on building Grid
Services
• UK Level 3 Grid deployment
• Future• OGSA-compliance throughout• Incorporate “best-of-breed”
OGSA services• Develop some if necessary• Available outside Newcastle
• Initial release• September 2003 (now October)• Subsequent releases depending
on availability of resources
• Use the myGrid Web Services as test cases• Workflow Enactment Service• Notification Service
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myGrid Workflow Enactment Service
• Produced by IT-Innovations (Southampton)• Supports WSFL, SCUFL
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myGrid Workflow Enactment Service
Workflow Enactment Service
Workflow ID
Consumer
Submit workflow
Workflow Enactment Service
Completed
Consumer
Workflow status (+ workflow ID)
Factory
Locator
Consumer
Create new instance
Workflow Enactment Grid Service Instance
ok
Consumer
Submit workflow
Workflow Enactment Grid Service Instance
Completed
Consumer
Workflow Status
Web Service Grid Service
Could have used extensibility to submit the workflow as part of the instantiation
process
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myGrid Workflow Enactment Service
• Experiences• Enactment engine just a jar
• 23 external jar dependencies
• Could have used the same interface, exposing the Workflow ID• Interface specific to the myGrid project – no GGF standard
• A different interface and BPEL support as part of an MSc project – same approach though
• Implementation quite simple• A new Grid Service was created that made direct calls to the engine• A Grid Service Instance representing each workflow
• Knowledge of OGSI architecture and concepts required• Time spent on learning GT3 and the available tools
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myGrid Notification Service
• Produced by University of Southampton• Publisher/Subscriber – Push/Pull• Of course, it could be consumed as is• Could be converted to a very simple Grid Service
• A Grid Service Instance just provides the same interface – No lessons to be learned
• OGSI defines the optional Notification portType• Expose topics as SDEs• Still provide operations for pulling messages• Significant changes
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myGrid Notification Service
Notification Service
Topics
Subscriber
Get list of topics
Notification Service
ok
Subscriber
Subscribe (topic, subscriber info)
Notification ServiceDelivery
Subscriber
PublisherPublish message
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myGrid Notification Service
Notification Grid Service Instance
SDEs names
Subscriber
Read SDEs names
Notification Grid Service Instance
ok
Subscriber
Subscribe to SDE (GSR)
Notification Grid Service Instance
DeliverySubscriber
SubscriberPublish messagePublisher
Publisher
“Root” or “persistent” service
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myGrid Notification Service
• Experiences• Notification Service implemented as a servlet
• Dependencies on mysql, OpenJMS, Tomcat• Versioning nightmare if to be combined with other services
• Very difficult to use the servlet directly• A Grid Service Instance sends SOAP messages to the local
Notification Service• A Grid Service Instance is created for each subscription• Interface compatible with OGSI• Implementation time-consuming (still in progress)• Knowledge of OGSI architecture and concepts required• Time spent on learning GT3 and the available tools
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Issues to consider
• Performance• Security• Interface and operation extensibility
• Scope of service instances• Represent workflow execution• Stateful interactions with Notification service, subscription as a
service instance
• SDEs• Lifetime and granularity• Service instance sharing• Stateful interactions
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Consumer
Contextualisation
Contextualisation as the means to create the logical unit of work
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Conclusions
• Experience in moving from Web Services to Grid Services• Smaller, existing projects difficult to persuade• Larger projects, like myGrid, are considering• New projects, like GOLD, keen• Workflow
• “Named” workflows using a GSH• Stateful interactions with a “named” workflow• Expose workflow status through an SDE
• Notification• OGSI-standard interface• Topics as SDEs (not very flexible)
• Value in such a transition?• Cost of learning OGSI/OGSA, GT3 or other implementation• Costs of porting/wrapping
• Are Web Services enough to build Grid applications?• Look at the Grid Application Framework based on Web Services
Specifications and Practices document (http://www.neresc.ac.uk/ws-gaf)