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Dec 20, 2022 324 likes •664 views

W eb Services and the Grid W eb Services and the Grid Supercomputing, Visualization & e-Science Manchester Com puting W SRF and W SRF::Lite W SRF::Lite W SRF and Mark Mc Keown WSRF: : Lite developer Formerly UK Grid Support

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Manchester Com puting

Supercomputing, Visualization & e-Science

Mark Mc Keown WSRF: : Lite developer Formerly UK Grid Support Center Mark.McKeown@manchester.ac.uk

W eb Services and the Grid W eb Services and the Grid – – W SRF and W SRF and W SRF::Lite W SRF::Lite

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Topics.

Grid Web Services WSRF WSRF::Lite

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What is a Grid…

[…provides] "Flexible, secure, coordinated resource sharing among dynamic collections of individuals, institutions, and resource"

– “The Anatomy of the Grid”

"…is distributed computing across multiple administrative domains"

– Dave Snelling.

“…internet scale distributed computing…” Etc…

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Distributed Systems…

M e s s a g e M e s s a g e Message M e s s a g e Message

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Designing a Distributed System…

Design the messages. Design the message exchange patterns. What are the pink blobs?

– Computer systems, processes on a system, institutes, objects, resources, State Machines?

Deal with latency, concurrency, partial failure etc…

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Web Services

“A Web service is a software system designed to support

interoperable machine-to-machine interaction over a network.”

“It has an interface described in a machine-processable format

(specifically WSDL).”

“Other systems interact with the Web service in a manner

prescribed by its description using SOAP messages, typically conveyed using HTTP with an XML serialization in conjunction with other Web-related standards.” W3C – Web Services Architecture

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SOAP over HTTP

HTTP HEADERS

Some XML… Some XML… < Envelope> < /Envelope> < Header> < /Header> < Body> < /Body>

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OGSI – The Grid Service I nstance

“A Grid service instance is a (potentially transient) service that conforms to a set of conventions, expressed as WSDL interfaces, extensions and behaviours, for such purposes as lifetime management, discovery of characteristics, and notification.” “Grid services provide for the controlled management of distributed and often long-lived state that is commonly required in sophisticated distributed applications”. “Anatomy of the Grid”

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Why OGSI didn’t succeed…

Too much stuff in one specification. Does not work well with existing Web service and XML tooling. Too object orientated. (see ”A Note on Distributed Computing” by Waldo et al. for a critique of distributed object systems)

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WSRF Web Service Resource Framework

WSRF effectively has replaced OGSI since January 2004. Addresses the issues with OGSI.. Simply a re-factoring of OGSI – I wish Instead of Grid Service Instances we have WS-Resources.

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Implied Resource Pattern

Client WS-Resource WS-Resource WS-Resource Web Sevice

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SOAP

POST http://vermont.man.ac.uk/Counter

< Envelope> < Header> < counterID> 12342-dsfgsdfg< /counterID> … < /Header> < Body> < add> < value> 10< /value> < /add> < /Body> < /Envelope>

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Creating a new WS-Resource

Client Web Sevice WS-Resource WS-Resource WS-Resource create EPR

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WS-Addressing EndPoint Reference EPR

<EndpointReference> <Address>http://vermont.man.ac.uk/Counter</Address> <ReferenceProperties> <counterID>12342-dsfgsdfg</counterID> </ReferenceProperties> </EndpointReference>

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WSRF Family of Specifications

WS-ResourceProperty WS-ResourceLifetime WS-BaseFaults WS-ServiceGroup WS-RenewableReferences (not yet released)

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WS-ResourceProperty

Provides a “projection” of the WS-Resource’s state. The ResourceProperties are described in an XML document – the WSDL for the service should have a pointer to this document. GetResourceProperty and GetMultipleResourceProperties

perations allows client to query the state of the WS-Resource

SetResourceProperty operation allows client to modify the state

f the WS-Resource – supports Insert, Delete and Update.

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ResourceProperty Document

<xs:schema …..> <xs:element name=“foo” xsd:type=“int” />* <xs:element name=“bar” xsd:type=“string” />? <xs:element name=“count” xsd:type=“int” />? </xs:schema>

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WS-ResourceLifetime

Unlike OGSI, lifetime management is optional in WS-RF. Destroy and SetTerminationTime operations allows the client to control the lifetime of the WS-Resource. The lifetime of the WS-Resource is just another WS- ResourceProperty – can use GetResourceProperty to find termination time. However you CANNOT set the termination time through the SetResourceProperty operation – must use SetTerminationTime!!

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WS-BaseFaults

A standard way to report errors: <BaseFault> <Timestamp>…</Timestamp> <OriginatorReference>…</OriginatorReference>? <ErrorCode>…</ErrorCode>? <Description>…</Description>* <FaultCause>…</FaultCause>* </BaseFault>

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WS-ServiceGroup

Mechanism to group a set of WS-Resources together – basic building block for registries. WS-Resources come and go, need to garbage collect stale entries in the ServiceGroup – but how? When we register a WS-Resource in a ServiceGroup a new WS-Resource is created by the ServiceGroup. The sole purpose of this new WS-Resource is to control the lifetime of the entry in the ServiceGroup – destroy this WS-Resource and the entry disappears.

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WS-ServiceGroup

Client ServiceGroupEntry ServiceGroupEntry

WS-ServiceGroup

ServiceGroupEntry Add WS-Resource Destroy WS-Resource WS-Resource

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Other WS Options for building Grids

WS-I. (http://www.ws-i.org/) REST, Representational State Transfer.

(http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm)

WS-Transfer.

(http://msdn.microsoft.com/library/en-us/dnglobspec/html/ws-transfer.pdf)

MEST.

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WSRF: : Lite

OGSI::Lite, the pre-curser to WSRF::Lite, started out as an exercise to understand OGSI and the concepts behind Grid Services. The name is derived from SOAP::Lite the excellent Web Service module written by Pavel Kulchenko on which WSRF::Lite is built. “Don’t be mislead by the Lite suffix – this refers to the effort it takes to use the module, not its capabilities” Pavel Kulchenko

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Perl – Are you mad?

“If Perl is the solution, you’re solving the wrong problem.” Erik Naggum. “Perl as a language has less a design than a thousand special features flying in close formation.” “Perl: the first post-modern computer language.” Larry Wall.

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Apache CGI Script

#! /usr/bin/perl -w use SOAP::Transport::HTTP; SOAP::Transport::HTTP::CGI

>dispatch_to( ‘/home/zzcgumk/modules’ )
>handle;

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Simple Service

package HelloWorld; sub Hello { my ($self, $name) = @_; return "Hello ".$name; } 1;

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Simple Client

#! /usr/bin/perl use SOAP::Lite; my $service = SOAP::Lite- >service( "URLtoWSDL" ); my $ans = $service- >Hello( "Mark" ); if ($ans- >fault) { die $ans- >faultstring } print $ans- >result."\n";

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WSRF: : Lite Supports…

WS-Addressing WS-ResourceProperties WS-ResourceLifetimes WS-BaseFaults WS-ServiceGroups

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WSRF: : Lite

WS-Resources can be hosted in the WSRF::Lite Container, Apache or using a simple standalone script. A WS-Resource simply inherits the core WSRF functionality from a base module. The WS-Resource state is stored and managed using either: – A Process. – A Database. – A File.

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WSRF: : Lite

CLIENT SOAP HTTP CLIENT SOAP HTTP Process

SOAP/ HTTP Unix-Socket

Process

SOAP/ HTTP Unix-Socket

File DB

ODBC

WSRF::Lite Container Or Apache

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Security

Currently the Container scripts support Transport Layer Security through HTTPS with x509 certificates. If the WS-Resources are hosted using GridSite then authentication using GSI proxy certificates is possible. Plan to implement WS-Security – unclear how this will work

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Questions?

“…I still think the WS-* stack is bloated, opaque, and insanely

complex. I think it’s going to be hard to understand, hard