1. Additional Features of WSRF/GT4 Services
A brief outline
Slides for Grid Computing: Techniques and Applications by Barry Wilkinson, Chapman & Hall/CRC press, © 2009.
Chapter 7, pp For educational use only. All rights reserved. Sept 14, 2009
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2. Stateful GT 4 Grid Services Review
“Pure” Web services are stateless.
Stateful web services required for Grid computing.
WSRF provides stateful web services by having a Web service as a front-end to a stateful “resource.”
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3. GT 4 services
Key aspect is separation of (Web) service and a resource – conceptually if not actually.
Provides ability to have “state” without altering the statelessness of Web service.
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4. Web Service Resource Framework
(WSRF)‏
Resource
Web Service
Resource properties
Holds information retained between accesses.
Client
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5. Resource properties Name given to data items in the resource
Can consist of:
Data values about current state of service (results of calculations etc.)‏
Metadata: Information about data
Information about whole resource: Termination time, etc.
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6. Combined Service Code and Resource
Simplest arrangement is to have both the service code and resource code were held in a single file.
Ideally, we would like to have multiple resources for a Web service
Having one file not the preferred way except for simple service examples.
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7. Separate Resource More generally, resource is a (stateful) class.
End Point Reference (EPR) is an XML document that has URL of service and possibly a resource identification (key)‏
Classes provided for different arrangements:
ReflectionResourceProperty class can be used when service code and resource in one file.
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8. Resource Home Resources are managed by Resource Home's
Provides resource management functions
for adding resources
for removing resources
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9. Resource Home Resource home Web Service Client
create/
find resource
Web Service
Client
Manages
Client only interacts with stateless web service
Methods operate on resources properties
Resource
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10. Service and resource code
Resource home
create/
find resource
Web Service
Client
Manages
void add(int a)‏
void subtract (int a)‏
Resource
int value
String lastOP
add() and subtract() methods operate on resource properties
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11. Resource Home Resource home Web Service Client Resource
If service and resource in one file, resource limited to one resource using a Globus supplied resource home called ServiceResourceHome
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12. Service and resource code
Resource home
“ServiceResourceHome”
Web Service
create/
find resource
void add(int a)‏
void subtract (int a)‏
Client
ServiceResourceHome returns service object
Resource
int value
String lastOP
add() and subtract() methods operate on resource properties
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13. Separately service, resource and resource home files
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14. Separate Service, Resource & Resource Home files Singleton Resources (Single resource)‏
Web Service
Client
void add(int a)‏
void subtract (int a)‏
int value
String lastOP
Resource
Three files: the service, the resource home, and the resource.
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15. Multiple Resources
Suppose there are multiple resources that a service might interact with:
Resources
Web Service
Client
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16. Creating Resources WS-Resource Factory Pattern
Traditional object-oriented approach to creating resources is to use a “factory” service:
Factory service responsible for creating instances of resources.
Each resource assigned a unique “key”, which together with service URI identifies WS-resource pair. (Endpoint Reference)‏
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17. Request operation on resource
WS-Resource Factory Pattern
Factory service
Resources
Request resource creation
Return WS-Resource EPR
Create
Request operation on resource
Perform operation
Client
“Instance” Service
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18. Relationship with Resource Home
Factory Service
Use Resource Home to create resource
Request resource creation
Resource Home
Find resource
Service instance
Client
Manages
Request operation
Resource
Methods operate on resources properties
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19. endpointReference createResource()‏
Factory service Create Resource operation
endpointReference createResource()‏
Returns an EPR to the newly created WS- Resource.
“Fully qualified” EPR to include URI of service and key of resource
Client needs to know location of factory service.
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20. Question
Q: Why would one want to have multiple resources for a Web service?
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21. Lifecycle Management Lifecycle mechanisms available in WSRF.
GT4 provides mechanisms to specify when a resource is automatically destroyed.
Immediately by invoking destroy operation through a Web service
Scheduled some time in the future
Leased-based lifecycle management
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22. globus-wsrf-destroy -e EPR1234.epr math.destroy(new Destroy());
Immediate Destruction
Command line:
globus-wsrf-destroy -e EPR1234.epr
Destruction can be requested through a Web service by a client:
math.destroy(new Destroy());
Notice - factory responsible for creating resource, but service instance destroys it.
File containing EPR of resource
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23. wsrf-set-termination-time wsrf-set-termination-time -e EPR1234.epr 100
Scheduled Termination Time
Termination time exposed as a resource property.
Can be set with GT4 command:
wsrf-set-termination-time
Example
wsrf-set-termination-time -e EPR1234.epr 100
File containing EPR of resource
Termination time in seconds
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24. Question
Q: Why would one want to have a termination time set for a resource?
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25. Lease-based Lifetime
In lease-based model, resources must be kept alive by interested parties, otherwise resource dies.
A lifetime for a service is set after which the service is destroyed.
Interested parties (clients) must renew the lease (reset the termination time) or it will be destroyed.
Clean up without having to use a destroy operation explicitly.
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26. Notifications Notifying clients when something interesting happens.
Example might be when a resource property reaches a certain value
Could use polling but this is very inefficient.
WS-notification defines mechanisms.
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27. Resource property changes
Examples:
Changes to resource property values.
Methods added
Methods removed
Resources destroyed
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28. Subscribe for notifications
Need client to “subscribe” to receive notifications.
Subscriptions are for a particular topic.
Resource implemented with GT 4 classes that provide for automatic notifications whenever property changes.
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29. Automatic notifications
Fig 7.8
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30. GT 4 Information Services Monitoring and Discovery Services (MDS)
Principal components: Index service Trigger service WebMDS

31. Information services
WebMDS
Index service
Trigger service

32. Globus core does not include information services such as index services. When installed, would see it in list of services, e.g.:
Index service
Trigger service
Fig 7.9

33. (resources with resource properties)‏
Index Service
GT 4 provided with an index service that can maintain a list of available resources.
Container
Index service
(resources with resource properties)‏
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34. Index service
Note -- index service does not act as a local service registry listing the services — it act as a registry for the resources.
Fig 7.10
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35. “add” method of ResourceHome used to create resource.
Override method to include registering resource with index service.

36. Querying Index Service wsrf-query
Browse index service with the GT4 command:
wsrf-query
which will list resource properties in an XML format.
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37. Example wsrf-query –s http://localhost:8080/wsrf/services/
DefaultIndexService '/*'
which will list resource properties in an XML format.
Result might be:
<ns1:MyServiceResourceProperties xmlns:ns1= “...”>
<ns1:data>234</ns1:data>
</ns1:MyServiceResourceProperties>

38. An index service can be browsed with the GT4 command such as:
wsrf-query –s \
'/*'
which will list all the resource properties and their values in an XML format, where index service located at
XPath expressions can be used to select specific resource properties.

39. https://torvalds.cis.uncw.edu/wsrf/ services/DefaultIndexService
“Community” Index Service
A remote index service that holds all the index services of the “virtual organization.”
For example a community index service might be at:
services/DefaultIndexService
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40. Fig 7.12
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41. Community index service
Student 1 Index entry
Student 2 Index entry
Local Index service
Local Index service
Resources
Resources
Service
Client
Client
Service
Student 1 container
Student 2 container
Only container and GT 4 core needed at each site to handle services.
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42. Querying Community Index Service
Have Community Index Service running.
Use wsrf-query command:
$GLOBUS_LOCATION/bin/wsrf-query -s ices/DefaultIndexService '/*'
Should see contents of all local index services.
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43. Resource Discovery
The local and community index services can be searched for a particular resource property.
Since Resources properties are XML, can use “XPath” queries for searching and retrieval.
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44. XML Path Language (XPath)‏
W3C recommendation, 1999
A query language for search XML documents.
Queries formed by identifying a route to the desired data.
For details:
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45. MDS4 Trigger Service Subscribes to a set of resource properties
Evaluate that data against a set of pre- configured conditions (triggers)
When a condition matches, action occurs
is sent to pre-defined address
Website updated
From: Monitoring and Discovery in a Web Services Framework: Functionality and Performance of Globus Toolkit MDS4 Jennifer M. Schopf, Sept 11, 2006

46. WebMDS
Web-based interface to display resource property information. Front-end to index services.
Sample:
webmds?info=indexinfo&xsl=servicegroupxsl

47. More Information Book Globus Toolkit 4 Programming Java Services
Borja Sotomayor and Lisa Childer
Morgan Kaufmann, 2006.
On-line
GT4 services:
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48. What is a (WS) notification in Grid services?
(a) A mechanism of the GGF committee to inform the community of changes to the (WS) standard
(b) A mechanism for client to inform a Grid service of its existence
(c) A mechanism to inform a client of changes in the service or resource
(d) A final demand to pay your taxes
Fig 7-4
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49. What is the purpose of the Globus index service?
(a) To hold index variables for arrays
(b) To operate on an array of functions
(c) To maintain a list of available services
(d) To maintain a list of available resources
Fig 7-11
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50. Questions
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