7-2.1

Additional Features of WSRF/GT4 Services

A brief outline

© 2011 B. Wilkinson/Clayton Ferner. Fall 2011 Grid computing course. Modification date: July 20, 2011

Note: Globus version 5 does not include any GT4 web service components and this section may be less important in the future.

7-2.2

Stateful GT 4 Grid ServicesReview

• “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.”

7-2.3

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.

7-2.4

Web Service

Resource

Resource properties

Client

Web Service Resource Framework(WSRF)

Holds information retained between accesses.

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.

7-2.5

7-2.6

Combining 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.

7-2.7

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.

7-2.8

Resource Home

• Resources are managed by Resource Home's

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

7-2.9

Resource Home

Client Web Service

Resource home

Resource

Manages

Methods operate on resources properties

create/find resource

Client only interacts with stateless web service

7-2.10

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

7-2.11

Resource Home

Client Web Service

Resource home

Resource

If service and resource in one file, resource limited to one resource using a Globus supplied resource home called ServiceResourceHome

7-2.12

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

7-2.13

Separate Service, Resource & Resource Home files

Singleton Resources (Single resource)

Client Web Service

Resource home

Resource

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

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

int valueString lastOP

7-2.14

Multiple Resources

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

Client Web Service

Resources

7-2.15

Creating ResourcesWS-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)

7-2.16

Client“Instance” Service

Resources

WS-Resource Factory Pattern

Factory service

Request resource creation

Request operation

on resource

Create

Perform operation

Return WS-Resource EPR

7-2.17

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

7-2.18

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.

7-2.19

Question

Q: Why would one want to have multiple resources for a Web service?

7-2.20

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

7-2.21

Immediate DestructionCommand 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

7-2.22

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

7-2.23

Question

Q: Why would one want to have a termination time set for a resource?

7-2.24

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.

7-2.25

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.

7-2.26

Resource property changes

• Examples:

– Changes to resource property values.– Methods added– Methods removed– Resources destroyed

7-2.27

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.

7-2.28

Automatic notifications

Fig 7.8

7-2.29

GT 4 Information Services

Monitoring and Discovery Services (MDS)

Principal components:Index service

Trigger serviceWebMDS

7-2.30

Index service

WebMDS

Trigger service

Information services

Globus core does not include information services such as index services.

When installed, would see it in list of services, e.g.:

7-2.31

Index service

Trigger service

Fig 7.9

7-2.32

Container

Index service

(resources with resource properties)

Index ServiceGT 4 provided with an index service that can maintain a list of available resources.

Index service

Fig 7.10 7-2.33

Note -- index service does not act as a local service registry listing the services — it act as a registry for the resources.

7-2.34

• “add” method of ResourceHome used to create resource.• Override method to include registering resource with index

service.

7-2.35

Querying Index Servicewsrf-query

Browse index service with the GT4 command:

wsrf-query

which will list resource properties in an XML format.

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>

An index service can be browsed with the GT4 command such as:

wsrf-query –s \http://localhost:8080/wsrf/services/DefaultIndexService '/*'

which will list all the resource properties and their values in an XML format, where index service located at http://localhost:8080/wsrf/services/DefaultIndexService.

XPath expressions can be used to select specific resource properties.

7-2.38

“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:

https://torvalds.cis.uncw.edu/wsrf/services/DefaultIndexService

7-2.39Fig 7.12

7-2.40

Local Index service

Resources

Service Client

Local Index service

Resources

ServiceClient

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

7-2.41

Querying Community Index Service

Have Community Index Service running.

Use wsrf-query command:

$GLOBUS_LOCATION/bin/wsrf-query -s https://torvalds.cis.uncw.edu/wsrf/services/DefaultIndexService '/*'

Should see contents of all local index services.

7-2.42

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.

7-2.43

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

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

– Email is sent to pre-defined address

– Website updated

7-2.44From: Monitoring and Discovery in a Web Services Framework: Functionality and

Performance of Globus Toolkit MDS4 Jennifer M. Schopf, Sept 11, 2006

WebMDSWeb-based interface to display resource property information.

Front-end to index services.

Sample: http://mds.globus.org:8080/webmds/

webmds?info=indexinfo&xsl=servicegroupxsl

7-2.45

7-2.46

More Information

BookGlobus Toolkit 4 Programming Java Services

Borja Sotomayor and Lisa Childer

Morgan Kaufmann, 2006.

On-line

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

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

7-2.47SAQ 7-4

7-2.48

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

FAQ 7-11

Questions

7-2.49