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GT 4 grid services and their implementation

Advanced features:An overview

Topics:Resource home

Singleton resourceMultiple resources

NotificationsLifecycles

ITCS 4146/5146, UNC-Charlotte, B. Wilkinson, 2007 Feb. 22, 2007

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Stateful GT 4 Grid ServicesReview

• “Pure” Web services are stateless.

• Stateful web services required for grid computing.

• Obtained in WSRF by having a web service front-end to a stateful “resource.”

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Web Service

Resource

Resource properties

Client

Web Service Resource Framework(WSRF)

Holds information retained between accesses.

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GT 4 services

• Key aspect is the separation of the (web) service and a resource – conceptually if not actually.

• Provides the ability to have “state” without altering the statelessness of a web service.

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Assignment 4

• In Assignment 4, both service code and resource code held in a single file.

• End Point Reference (EPR) actually is only the URL of the service. Not necessary to have resource identification (key)

• Having one file not the preferred way except for simple service examples.

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Resource Home

• Resources are managed by “Resource Homes”

• Provides resource management functions– for adding resources– for removing resources

• Although hidden in Assignment 4 where resource and service were in one file, a Resource Home did exist.

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Resource Home

Client Web Service

Resource home

Resource

Manages

Methods operate on resources properties

create/find resource

Client only interacts with stateless web service

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Service and resource code

Client Web Service

Resource home

Resource

Manages

add() and subtract() methods operate on resource properties

create/find resource

void add(int a)void subtract (int a)

int valueString lastOP

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Resource Home

Client Web Service

Resource home

Resource

Previously, service and resource in one file and resource limited to one resource using a globus supplied resource home called ServiceResourceHome

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Service and resource code

Client

Web Service Resource home“ServiceResourceHome”

Resource

add() and subtract() methods operate on resource properties

create/find resource

void add(int a)void subtract (int a)

int valueString lastOP

ServiceResourceHome returns service object

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Separately service, resource and resource home files

Singleton Resources(Single resource)

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Resource Home

Client Web Service

Resource home

Resource

Three files: the service, the resource home, and the resource.

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AcknowledgementThe following applies to the code in the next five slides:

/** This file is licensed under the terms of the Globus Toolkit

Public License v3, found at http://www.globus.org/toolkit/legal/4.0/license-v3.html.

* * This notice must appear in redistributions of this file, with or

without modification. */

You will be able to find the files in your assignment 4 software installation at:

$EXAMPLES_DIR/org/globus/examples/servives/core/singleton/imp/

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package org.globus.examples.services.core.singleton.impl;import org.globus.wsrf.Resource;import org.globus.wsrf.impl.SingletonResourceHome;public class MathResourceHome extends SingletonResourceHome {

public Resource findSingleton() {try {// Create a resource and initialize it.MathResource mathResource = new MathResource();mathResource.initialize();return mathResource;} catch (Exception e) {return null;}

}}

Singleton Resource home codeMathResourceHome.java

Implemented by extending SingletonResourceHome class.

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/*

public class MathService {/* Private method that gets a reference to the resource specified in the * endpoint reference. */private MathResource getResource() throws RemoteException {

Object resource = null;try {

resource = ResourceContext.getResourceContext().getResource();} catch (NoSuchResourceException e) {

throw new RemoteException("Specified resource does not exist", e);} catch (ResourceContextException e) {

throw new RemoteException("Error during resource lookup", e);} catch (Exception e) {

throw new RemoteException("", e);}MathResource mathResource = (MathResource) resource;return mathResource;

}

MathService codeMathService.java

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/*

/* Implementation of add, subtract, and getValue operations */

public AddResponse add(int a) throws RemoteException {

MathResource mathResource = getResource();

mathResource.setValue(mathResource.getValue() + a);

mathResource.setLastOp("ADDITION");

return new AddResponse();

}

public SubtractResponse subtract(int a) throws RemoteException {

MathResource mathResource = getResource();

mathResource.setValue(mathResource.getValue() - a);

mathResource.setLastOp("SUBTRACTION");

return new SubtractResponse();

}

public int getValueRP(GetValueRP params) throws RemoteException {

MathResource mathResource = getResource();

return mathResource.getValue();

}

}

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public class MathResource implements Resource, ResourceProperties {/* Resource Property set */private ResourcePropertySet propSet;/* Resource properties */private int value;private String lastOp;/* Initializes RPs */public void initialize() throws Exception {

this.propSet = new SimpleResourcePropertySet(MathConstants.RESOURCE_PROPERTIES);

ResourceProperty valueRP = new ReflectionResourceProperty(MathConstants.RP_VALUE, "Value", this);

this.propSet.add(valueRP);setValue(0);ResourceProperty lastOpRP = new

ReflectionResourceProperty(MathConstants.RP_LASTOP, "LastOp", this);

this.propSet.add(lastOpRP);setLastOp("NONE");

}

Resource codeMathResource.java

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/* Get/Setters for the RPs */public int getValue() {

return value;}public synchronized void setValue(int value) {

this.value = value;}public String getLastOp() {

return lastOp;}public synchronized void setLastOp(String lastOp) {

this.lastOp = lastOp;}/* Required by interface ResourceProperties */public ResourcePropertySet getResourcePropertySet() {

return this.propSet;}

}

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Multiple Resources

Suppose there are multiple resources that a service might interact with:

Client Web Service

Resources

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Creating Resources

WS-Resource Factory Pattern

A traditional object-oriented approach to creating resources is to use a “factory” service:

The factory service is responsible for creating instances of objects.

Each resource will be assigned a unique “key”, which together with the service URI identifies the WS-resource pair. (Endpoint Reference)

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Client “Instance” Service

Resources

WS-Resource Factory Pattern

Factory service

Request resource creation

Request operation on resource

Create

Perform operation

Returns WS-Resource EPR

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Relationship with Resource Home

Client Service instance

Resource Home

Resource

Manages

Methods operate on resources properties

Find resource

Factory Service

Request resource creation

Use Resource Home to create resource

Request operation

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Factory serviceCreate 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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WS-Addressing Terms

Endpoint – the destination where the web service can be accessed.

Endpoint reference, EPR –describes the destination, and includes the destination location as URI, but can have other parameters

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Endpoint reference, EPR

Like all WS-* specs, defined in terms of XML.

Defined as complex type. Can contain:• Address (a URI) (required)• Reference Properties• Reference Parameters• Port type• Service name• Policy elements

Corresponds to portType and service of WSDL document

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Minimum is simply service address, using <wsa:Address> tag:

<wsa:EndpointReference>

<wsa:Address>

http://www.cs.uncc.edu/axis/abw/Myservice.jws

</wsa:Address>

</wsa:EndpointReference>

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Reference Properties <wsa:ReferenceProperties>

Used to identify resource properties in EPR:

<wsa:EndpointReference>

<wsa:Address>

http://www.cs.uncc.edu/axis/abw/Myservice.jws

</wsa:Address>

<wsa:ReferenceProperties> <resourceID>28</resourceID> </wsa:ReferenceProperties>

</wsa:EndpointReference>

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Another example file containing Endpoint Reference

<StickyNoteEndpoint xsi:type="ns1:EndpointReferenceType"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:ns1="http://schemas.xmlsoap.org/ws/2004/03/addressing">

<ns1:Address

xsi:type="ns1:AttributedURI">http://192.168.1.100:8080/wsrf/

services/

StickyNoteService

</ns1:Address>

<ns1:ReferenceProperties “xsi:type="ns1:ReferencePropertiesType">

<ns1:NoteKey xmlns:ns1="http://sticky.com">25781085

</ns1:NoteKey>

</ns1:ReferenceProperties>

<ns1:ReferenceParameters xsi:type="ns1:ReferenceParametersType"/>

</StickyNoteEndpoint>

Resource “key”

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SOAP messageWS-Addressing requires that contents of: <wsa:Address> and <wsa:ReferenceProperties>must appear in SOAP’s header:

<soap:Envelop><soap:Header>... <wsa:To>http://www.cs.uncc.edu/axis/abw/Myservice.jws</wsa:To> <resourceID>28</resourceID>...</soap:Header>

<soap:Body> ...</soap:Body>

</soap:Envelop>

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Index Service

• GT 4 provided with an index service that can maintain a list of available services.

• Index service acts as local service registry.

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Container

Index service

Multiple services/Resources(with resource properties)

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Querying Index Servicewsrf-query

Browse index service with the GT4

wsrf-query command:

$GLOBUS_LOCATION/bin/wsrf-query -s http://localhost:8080/wsrf/services/DefaultIndexService '/*'

which will list the services in an XML format.

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“Community” Index Service

• A remote index service is used, which holds all the services of the “virtual organization.”

• Last year we located a community index service at:

http://beowulf.bear.uncw.edu:8080/wsrf/services/DefaultIndexService

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Local Index service

Resources

Community index service

beowulf.bear.uncw.edu:8080/wsrf/services/

DefaultIndexService

Service

client

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Implementation

• Configure local index to register with community index service.

• All local information, including service resource properties, copied to community index service.

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Querying Community Index Service

Have Community Index Service running.

Use wsrf-query command:

$GLOBUS_LOCATION/bin/wsrf-query -s http://beowulf.bear.uncw.edu:8080/wsrf/services/DefaultIndexService '/*'

Should see contents of all local index services.

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Local Index service

Resources

Service

client

Local Index service

Resources

Service

client

Student 1 Index entry

Student 2 Index entry

Student 1 container

Only container and GT 4 core needed at each site to handle services.

Student 2 container

Community index service

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NotificationsNotifying clients when something interesting happens.

Example might be when a resource property reaches a certain value

Could be found out by polling resource but that would be very inefficient.

WS-notification provides mechanisms.

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Notifications

• Notifications, generally, are a means by which a client can be informed of changes that have occurred such as:– Changes to resource property values.– Methods added– Methods removed– Resources destroyed

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Clients

Service

“watch” service

Serviceresource property

Notification that property changed

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• Need the client to “subscribe” to receive notifications.

• Subscriptions are for a particular topic.

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Implementation

• Add subscribe operation to wsdl file.

• Add SubscribeProvider to wsdd file.

• Modify <service_code>.java

• Modify post-deploy.xml file

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Lifecycle ManagementGT4 provides mechanisms to specify when a

resource is destroyed:

• Immediately by invoking destroy operation

• Scheduled some time in the future – leased-based lifecycle management

• Lease periodically renewed otherwise resource destroyed within a specified time.

• Lifecycle mechanisms available in WSRF.

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Lease-based Lifetime

• In lease-based model, resources must be kept alive by interested parties, otherwise resource dies.

• Set a lifetime for a service after which the service is destroyed.

• Clean up without having to use a destroy operation explicitly.

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Termination TimeTermination time exposed as a resource property.

Can be set with GT4

wsrf-set-termination-time command.

Example

$GLOBUS_LOCATION/bin/wsrf-set-termination-time -e note--1234.epr 100

File containing EPR of resource

Termination time in seconds

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Resource Discovery

• Local and community index services can be searched for information

• Since Resources properties are XML, can use “XPath” queries for searching and retrieval.

• Uses a “XPath” query (apparently embedded in a script called search-note in this exercise)

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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: http://www.w3.org/TR/xpath

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More Information

• GGF: http://www.ggf.org

• GT4 services: http://gdp.globus.org/gt4-tutorial/

• GT4 tutorial by Foster:http://www.globus.org/toolkit/docs/4.0/key/GT4_Primer_0.6.pdf

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Book

Globus Toolkit 4 Programming Java Services

Borja Sotomayor and Lisa Childer

Morgan Kaufmann, 2006.