Community Grids Architecture Discussion

Internal Discussion

August 20 2004

Geoffrey Fox

Community Grids Lab

Indiana University

gcf@indiana.edu

Philosophy of Web Service Grids• Much of Distributed Computing was built by natural

extensions of computing models developed for sequential machines

• This leads to the distributed object (DO) model represented by Java and CORBA– RPC (Remote Procedure Call) or RMI (Remote Method

Invocation) for Java• Key people think this is not a good idea as it scales badly

and ties distributed entities together too tightly– Distributed Objects Replaced by Services

• Note CORBA was considered too complicated in both organization and proposed infrastructure– and Java was considered as “tightly coupled to Sun”– So there were other reasons to discard

• Thus replace distributed objects by services connected by “one-way” messages and not by request-response messages

Web services• Web Services build

loosely-coupled, distributed applications, based on the SOA principles.

• Web Services interact by exchanging messages in SOAP format

• The contracts for the message exchanges that implement those interactions are described via WSDL interfaces.

Databases

Humans

ProgramsComputational resources

Devices

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<env:Envelope> <env:Header> ... </env:header> <env:Body> ... </env:Body></env:Envelope> m

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AP

and

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SOAP messages

Importance of SOAP• SOAP defines a very obvious message structure

with a header and a body• The header contains information used by the

“Internet operating system”– Destination, Source, Routing, Context, Sequence

Number …

• The message body is only used by the application and will never be looked at by “operating system” except to encrypt, compress it etc.

• Much discussion in field revolves around what is in header!– e.g. WSRF adds a lot to header

Web Services• Java is very powerful partly due to its many “frameworks” that

generalize libraries e.g.– Java Media Framework– Java Database Connectivity JDBC

• Web Services have a correspondingly collections of specifications that represent critical features of the distributed operating systems for “Grids of Simple Services”– Some 60 active WS-* specifications for areas such as– a. Core Infrastructure Specifications– b. Service Discovery– c. Security– d. Messaging– e. Notification– f. Workflow and Coordination– g. Characteristics– h. Metadata and State

WS-I Interoperability• Critical underpinning of Grids and Web Services is the

gradually growing set of specifications in the Web Service Interoperability Profiles

• Web Services Interoperability (WS-I) Interoperability Profile 1.0a." http://www.ws-i.org. gives us XSD, WSDL1.1, SOAP1.1, UDDI in basic profile and parts of WS-Security in their first security profile.

• We imagine the “60 Specifications” being checked out and evolved in the cauldron of the real world and occasionally best practice identifies a new specification to be added to WS-I which gradually increases in scope– Note only 4.5 out of 60 specifications have “made it” in this

definition

Web Services Grids and WS-I+• WS-I Interoperability doesn’t cover all the capabilities need to

support Grids• WS-I+ is designed to minimal extension of WS-I to support

“most current” Grids: it adds support for– Enhanced SOAP Addressing (WS-Addressing)– Fault tolerant (reliable) messaging– Workflow as in IBM-Microsoft standard BPEL

• Security and Notification best practice and support will probably get added soon– There are Web Service frameworks here but various IBM v Microsoft v

Globus differences to be resolved

• Portlet-based User Interfaces could be added• UK OMII Open Middleware Infrastructure Institute is adopting

this approach to support UK e-Science program – Currently UK e-Science largely either uses GT2 (as in EDG) or Simple

Web Services for “database Grids”– http://www.omii.ac.uk/

Bit levelInternet

Layered Architecture for Web Services and Grids

Base Hosting EnvironmentProtocol HTTP FTP DNS …

Presentation XDR …Session SSH …

Transport TCP UDP …Network IP …

Data Link / Physical

ServiceInternet

Application Specific GridsGenerally Useful Services and Grids

Workflow WSFL/BPELService Management (“Context etc.”)

Service Discovery (UDDI) / InformationService Internet Transport Protocol

Service Interfaces WSDL

ServiceContext

HigherLevelServices

Working up from the Bottom• We have the classic (CISCO, Juniper ….) Internet routing the

flood of ordinary packets• Web Services build the “Service Internet” with

– Fault Tolerance (WS-RM not TCP)– Security (WS-Security not IPSec/SSL etc.)– Information Services (UDDI/WS-Context not

DNS/Configuration files)– At message/web service level and not packet/IP address

level• Software-based Service Internet useful as computers “fast”• Familiar from Peer-to-peer networks and built as a software

overlay network defining Grid (analogy is VPN)• On top of “Service Internet”, one supports dynamic context or

the “shared memory” supporting groups (from 2 to more) of services

Information Grid

Enterprise Grid

Compute Grid

Campus Grid

R2R1

Teacher

Students

Dynamic light-weight Peer-to-peerCollaboration Training Grid

4 Overlay NetworksWith a 5th superimposed

Consequences of Rule of the Millisecond• Useful to remember critical time scales

– 1) 0.000001 ms – CPU does a calculation– 2) 0.001 to 0.01 ms – MPI latency– 3) 1 to 10 ms – wake-up a thread or process– 4) 10 to 1000 ms – Internet delay

• 4) implies geographically distributed metacomputing can’t in general compete with parallel systems (OK for some cases)

• 3) << 4) implies RPC not a critical programming abstraction as it ties distributed entities together and gains a time that is typically only 1% of inevitable network delay – However many service interactions are at their heart RPC but

implemented differently at times e.g. asynchronously• 2) says MPI is not relevant for a distributed environment as low

latency cannot be exploited• Even more serious than using RMI/RPC, current Object paradigms

also lead to mixed up services with unclear boundaries and autonomy• Web Services are only interesting model for services today

Linking Modules

From method based to RPC to message based to event-based

Module A

Module B

Method Calls.001 to 1 millisecond

Service A

Service B

Messages

0.1 to 1000 millisecond latency

Coarse Grain Service ModelClosely coupled Java/Python …

Service B Service A

PublisherPost Events

“Listener”Subscribe to Events

Message Queue in the Sky

What is a Simple Service?• Take any system – it has multiple functionalities

– We can implement each functionality as an independent distributed service

– Or we can bundle multiple functionalities in a single service• Whether functionality is an independent service or one of many

method calls into a “glob of software”, we can always make them as Web services by converting interface to WSDL

• Simple services are gotten by taking functionalities and making as small as possible subject to “rule of millisecond”– Distributed services incur messaging overhead of one (local) to

100’s (far apart) of milliseconds to use message rather than method call

– Use scripting or compiled integration of functionalities ONLY when require <1 millisecond interaction latency

• Apache web site has many projects that are multiple functionalities presented as (Java) globs and NOT (Java) Simple Services– Makes it hard to integrate sharing common security, user profile,

file access .. services

What is a Grid I?• You won’t find a clear description of what is Grid and how

does differ from a collection of Web Services– I see no essential reason that Grid Services have different

requirements than Web Services– Geoffrey Fox, David Walker, e-Science Gap Analysis, June 30

2003. Report UKeS-2003-01, http://www.nesc.ac.uk/technical_papers/UKeS-2003-01/index.html.

– Notice “service-building model” is like programming language – very personal!

• Grids were once defined as “Internet Scale Distributed Computing” but this isn’t good as Grids depend as much if not more on data as well as simulations

• So Grids can be termed “Internet Scale Distributed Simple Services” and represent a way of collecting services together in same way that program (package) collects methods and objects together.

What is a Grid II?

• So we build collections of Web Services which we package as component Grids– Visualization Grid– Sensor Grid– Utility Computing Grid– Person (Community) Grid– Earthquake Simulation Grid– Control Room Grid– Crisis Management Grid

• We build bigger Grids by composing component Grids using the Service Internet

Grids of Grids of Simple Services• Link via methods messages streams• Services and Grids are linked by messages• Internally to service, functionalities are linked by methods• A simple service is the smallest Grid• We are familiar with method-linked hierarchy

Lines of Code Methods Objects Programs Packages

Overlayand ComposeGrids of Grids

Methods Services Component Grids

CPUs Clusters ComputeResource Grids

MPPs

DatabasesFederatedDatabases

Sensor Sensor Nets

DataResource Grids

Critical Infrastructure (CI) Grids built as Grids of Grids

Gas Servicesand Filters

Physical Network

Registry Metadata

Flood Servicesand Filters

Flood CIGrid Gas CIGrid… Electricity CIGrid …

Data Access/Storage

Security WorkflowNotification Messaging

Portals Visualization GridCollaboration Grid

Sensor Grid Compute GridGIS Grid

Core Grid Services

Database Database

Analysis and VisualizationPortal

RepositoriesFederated Databases

Data Filter

Services

Field Trip DataStreaming Data

Sensors

?DiscoveryServices

SERVOGrid

ResearchSimulations

Research Education

CustomizationServices

From Research

to Education

EducationGrid ComputerFarmGeoscience Research and Education Grids

GISGrid

Sensor GridDatabase Grid

Compute Grid

Minicomputer

Firewall

ComputerServer

PDA

Modem

Laptop computerWorkstationPeers

Peers

Audio/VideoConferencing Client

Audio/VideoConferencing Client

NaradaBrokering BrokerNetwork

NaradaBrokering

Web Service B

Stream

Server-enhanced Messaging

NB supports messagesand streams

Queues

Multiple transport supportIn publish-subscribeParadigm with differentProtocols on each link

Transport protocols supported include TCP,  Parallel TCP streams, UDP, Multicast, SSL, HTTP and HTTPS.Communications through authenticating proxies/firewalls & NATs. Network QoS based Routing

Subscription Formats Subscription can be Strings, Integers, XPath queries, Regular Expressions, SQL and tag=value pairs.

Reliable delivery Robust and exactly-once delivery of messages in presence of failures

Ordered delivery Producer Order and Total Order over a message type Time Ordered delivery using Grid-wide NTP based absolute time

Recovery and Replay Recovery from failures and disconnects.Replay of events/messages at any time.

Security Message-level WS-Security compatible security

Message Payload options

Compression and Decompression of payloadsFragmentation a nd Coalescing of payloads

Messaging Related Compliance

Java Message Service (JMS) 1.0.2b compliant Support for routing P2P JXTA interactions.

Grid Application Support NaradaBrokering enhanced Grid-FTP. Bridge to the Globus TK3.

Web Service reliability Prototype implementation of WS-ReliableMessaging

Current NaradaBrokering Features

IOI and CIE• Let us study the two layers IOI (Service Internet On the Bit Internet)

and CIE (Context and Information Environment)• IOI is most “straightforward” as it is providing reasonably well

understood capabilities at a new “level”• CIE is roughly the inter-service “shared memory” used to manage and

control them at “distributed operating system level– Critical is “shared” (a database service) versus message based CIE

IOI

Application Specific GridsGenerally Useful Services and Grids

Workflow WSFL/BPELService Management (“Context etc.”)

Service Discovery (UDDI) / InformationService Internet Transport Protocol

Service Interfaces WSDL

CIE

HigherLevelServices

NaradaBrokering and IOI• “Software Overlay Network” features• Support for Multiple Transport protocols• Support for multiple delivery mechanisms

– Reliable Delivery– Exactly-once Delivery– Ordered Delivery– Optional Delivery optimization modules for different modes

• Compression/Decompression of payloads with optional module

• Coalescing/Fragmentation of payloads with optional module

• NTP Time Service• Security Service with optional module• Virtual Private Grid

Virtualizing Communication Communication specified in terms of user goal and Quality of

Service – not in choice of port number and protocol Bit Internet Protocols have become overloaded e.g. MUST use

UDP for A/V latency requirements but CAN’t use UDP as firewall will not support ………

A given “Service Internet” communication can involve multiple transport protocols and multiple destinations – the latter possibly determined dynamically

Dial-upFilter

SatelliteUDP

FirewallHTTP

A

B1

Hand-HeldProtocol

FastLink

Software MulticastB2

B3NB Broker Client Filtering

NB Brokers

NaradaBrokering and IOI• Optimization of Messaging Environment (Broker set up

etc.) using CIE • Support of WS-FlexibleRepresentation (see later) in

transport of Streams• Performance Monitoring• Performance optimized routing with optional module• Ad-hoc Network Support• Broker Discovery --Find nearest broker• Topic discovery• SOAP Support and integration with WSIF, Axis, WSE,

gSOAP, Java WSDP• Support for WS-Reliability, WS-ReliableMessaging and

their Federation• Congestion control and other optimizing message delivery

strategies

Performance Monitoring Every broker incorporates a Monitoring service that

monitors links originating from the node. Every link measures and exposes a set of metrics

• Average delays, jitters, loss rates, throughput. Individual links can disable measurements for

individual or the entire set of metrics. Measurement

intervals can also be varied

Monitoring Service, returns measured metrics to Performance Aggregator.

BrokerNode

LinkData

BrokerNode

LinkData

Performance AggregationService

Control MessageExchange

Aggregates infofrom nodes in acertain domain

MonitoringService

NaradaBrokering Service IntegrationS1 S2P2P1

S1 S2

S1 S2

Proxy Messaging

Handler Messaging

Notification

S? Service P? Proxy

NB Transport

Internal to Service: SOAP Handlers/Extensions/Plug-ins Java (JAX-RPC) .NET Indigo and special cases: PDA's  gSOAP, Axis C++

Standard SOAP Transport

Any Transport

Mechanisms for Reliable Messaging I

• There are essentially sequence numbers on each message• Unreliable transmission detected by non-arrival of a

message with a particular sequence number• Remember this is “just some TCP reliability” built at

application level• One can either use ACK’s – Receiver (service B) positively

acknowledges messages when received– Service A fully responsible for reliability

• Or NAK’s – Service B is partially responsible and tracks message numbers – sends a NAK if sequence number missing

Service B Service A

M(n+1)M(n)

Mechanisms for Reliable Messaging II• Each message has a retransmission time; messages are

retransmitted if ACK’s not received in time– Uses some increasing time delay if retransmit fails

• Note need to be informed (eventually) that OK to throw away messages at sender; pure NAK insufficient

• Note this is reliability from final end-point to beginning end-point: TCP reliability is for each link and has different grain size and less flexible reliability mechanisms

• There are several efficiency issues– Divide messages into groups and sequence within groups– Do not ACK each message but rather sequences of messages

• NAK based system attractive if high latency (some mobile devices) on messaging from receiver back to sender

Custom Message Reliability

NaradaBroker

Filter 1

Filter 2

WS-RM

WirelessOptimizedWS-RM

WS-Reliability

2 second PDA reply latency!

Different endpoints may well need different reliability schemes. Another reason to use application layer.Need to define easy touse “standard reliabilityprofiles

NaradaBrokering and Fault Tolerance• As well as reliable messaging, NaradaBrokering supports

performance based dynamic routing– Choose both route and protocol (UDP, Parallel TCP ..)

• It will also support automatic fail-over among replicated services subscribing to same message stream

• Provides scriptable control of streams for custom management schemes

• Saves ALL messages in faulttolerant storage for eithersession replay or recovery

• Will support reliable BitTorrent P2P file swapping model (better than GridFTP?)

GridFTP plus NaradaBrokering

Mirror Mirror on the wallWho is the fastest most reliable of them all?

Web Services!!!• Application layer “Internet” allows one to optimize message streams

and the cost of “startup time”, Web Services can deliver the fastest possible interconnections with or without reliable messaging

• Typical results from Grossman (UIC) comparing Slow SOAP over TCP with binary and UDP transport (latter gains a factor of 1000)

SOAP/XML WS-DMX/ASCII WS-DMX/Binary Record Count MB µ σ/µ MB µ σ/µ MB µ σ/µ

10000 0.93 2.04 6.45% 0.5 1.47 0.61% 0.28 1.45 0.38% 50000 4.65 8.21 1.57% 2.4 1.79 0.50% 1.4 1.63 0.27% 150000 13.9 26.4 0.30% 7.2 2.09 0.62% 4.2 1.94 0.85% 375000 34.9 75.4 0.25% 18 3.08 0.29% 10.5 2.11 1.11% 1000000 93 278 0.11% 48 3.88 1.73% 28 3.32 0.25% 5000000 465 7020 2.23% 242 8.45 6.92% 140 5.60 8.12%

Pure SOAP SOAP over UDP Binary over UDP

7020 5.60

SOAP Tortoise and UDP Hare II• Mechanism only works for streams – sets of related

messages• SOAP header in streams is constant except for

sequence number (Message ID), time-stamp ..• One needs two types of new Web Service

Specification• “WS-StreamNegotiation” to define how one can use

WS-Policy to send messages at start of a stream to define the methodology for treating remaining messages in stream

• “WS-FlexibleRepresentation” to define new encodings of messages

SOAP Tortoise and UDP Hare III• Then use “WS-StreamNegotiation” to negotiate stream in Tortoise

SOAP – ASCII XML over HTTP and TCP – – Deposit basic SOAP header through connection – it is part of

context for stream (linking of 2 services)– Agree on firewall penetration, reliability mechanism, binary

representation and fast transport protocol– Naturally transport UDP plus WS-RM

• Use “WS-FlexibleRepresentation” to define encoding of a Fast transport (On a different port) with messages just having “FlexibleRepresentationContextToken”, Sequence Number, Time stamp if needed– RTP packets have essentially this structure– Could add stream termination status

• Can monitor and control with original negotiation stream• Can generate different streams optimized for different end-points

CIE: Common Service Information and Metadata

• WS-RF and WS-GAF approach state with different approaches to contextualization – supplying a common “context” (Shared token or more generally (resource) metadata)

• One can supports such a common context either as pool of messages or as message-based access to a “database” (Context Service)

• We define a collection of services sharing information as a Gaggle

• Two services linked by a stream are perhaps simplest example of a Gaggle

CIE II• There is small amount of core shared information that must

be supported in the gaggle. This includes dynamic service metadata and the equivalent of configuration information.– We can put any “light-weight” information in the CIE even if it is

very application dependent• There are various metadata mechanisms suitable for “light-

weight dynamic situations”. WS-MetadataExchange, WS-Context and WSRF represent variants that can be supported.– UDDI, Globus MDS are “bigger” solutions

• The CIE stops short of supporting workflow; that would be built on top of CIE in analogous fashion to way that WS-CAF supports transactions as an extension of WS-Context.

• Note that there is a tension between storing metadata in messages and services. – This is shared versus distributed memory debate in parallel

computing

CIE III• We view the metadata as equivalent to some shared

memory for the services and whatever the actual implementation build a logical interface that is message based interactions with a simple database.

• There is a scripting environment that allows one to interact with administrative aspects of services and the support environment – it programs the Gaggle.

• Dennis Gannon notes that Linda (JavaSpaces) is an interesting model for the CIE at the Gaggle level.

• Notification Service is one simple CIE information tool

CIE in NaradaBrokering I• Scripting Management based on HPSearch technology• Topic discovery information repository• Broker discovery information repository• NaradaBrokering metadata information repository• Support of WS-FlexibleRepresentation information and

negotiation services• CIE Portal allowing access to all metadata, management of

deployment, firewall tunnels, performance info, error logs etc.– User and “programmatic” interfaces to set “defaults”

• Security Access and Authentication interface

CIE in NaradaBrokering II• Support of fault tolerant message storage, discovery and access

– Recovery– Replay or time difference sensitive recovery– Instant replay or replay of real-time streams– Support of finite state change architecture with major (complete) and minor

(partial) update events• Support of replicated services• Other core service fault tolerance mechanisms such as scalable

heartbeat• Support of multiple topic subscription types including string, integer,

XPath, Regular Expressions and <tag, value> tuples• JMS Compliance• Support of WS-Notification and WS-Eventing• Support of push and pull event models• Support for JXTA• Support for Gnutella• GridTorrent

CIE in NaradaBrokering III• Fault tolerant light weight metadata database (the core

metadata technology)• Support of WS-Discovery masquerading as dynamic UDDI• Support of WS-DM to manage services• Support of WSRF• Support of WS-Context• Support for WS-MetadataExchange• Support of session management aspects of XGSP, JXTA

Peer Groups etc.• GridFTP• FTHPIS

Web Service Metadata and State I• The Semantic Grid and Semantic Web are important

frameworks for metadata but handicapped by lack of “compelling” tools

• RDF Resource Description Framework (W3C) Set of recommendations expanded from original February 1999 standard http://www.w3.org/RDF/ and the heart of the Semantic Web and Grid http://www.semanticgrid.org

• DAML+OIL combining DAML (Darpa Agent Markup Language) and OIL (Ontology Inference Layer) (W3C) Note December 2001 http://www.w3.org/TR/daml+oil-reference

• OWL Web Ontology Language (W3C) Recommendation February 2004 http://www.w3.org/TR/2004/REC-owl-features-20040210/ More later!

Web Service Metadata and State II• WS-DistributedManagement Web Services Distributed Management

Framework with MUWS and MOWS below (OASIS) http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=wsdm

• Management includes issues like monitoring quality of service, enforcing service level agreements, controlling tasks and managing life-cycles.

• WSDM-MUWS Web Services Distributed Management: Management Using Web Services (OASIS) V0.5 Committee Draft April 2004 http://www.oasis-open.org/committees/download.php/6234/cd-wsdm-muws-0.5.pdf

• WSDM-MOWS Web Services Distributed Management: Management of Web Services (OASIS) V0.5 Committee Draft April 2004 http://www.oasis-open.org/committees/download.php/6255/cd-wsdm-mows-0.5-20040402.pdf

• WS-MetadataExchange Web Services Metadata Exchange (BEA,IBM, Microsoft, SAP) March 2004 http://www-106.ibm.com/developerworks/library/specification/ws-mex/– Describes how metadata can be exchanged between services rather

than by looking it up in registries like UDDI or higher level metadata catalogs; the old OGSI standard used such service-resident metadata extensively

Web Service Metadata and State III• WS-RF Web Services Resource Framework including WS-

ResourceProperties, WS-ResourceLifetime, WS-RenewableReferences, WS-ServiceGroup, and WS-BaseFaults (OASIS) http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=wsrf with Oasis TC set up April 2004 and V1.1 Framework March 2004 http://www-106.ibm.com/developerworks/library/ws-resource/ws-modelingresources.pdf – Uses rich metadata to define stateful interactions – its use of SOAP header

creates interoperability problems

• ASAP Asynchronous Service Access Protocol (OASIS)• http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=asap

with V1.0 working draft G June 2004 http://www.oasis-open.org/committees/download.php/7151/wd-asap-spec-01g.pdf

• WS-GAF Web Service Grid Application Framework (Arjuna, Newcastle University) http://www.neresc.ac.uk/ws-gaf/ – Uses WS-Context to provide “opaque” (don’t say much) stateful interactions

Metadata Catastrophe I• We keep finding places where metadata can be transmitted

to and from services• WS-Addressing and WS-RF specify metadata in SOAP

header of messages • WS-Context similarly specifies both SOAP header and WS-

Context context services as location of (temporary) metadata

• We have registries like UDDI of service data• WS-MetadataExchange covers metadata stored in services

– Service metadata is very common and often not explicitly called out e.g. WebDAV as in Apache Slide stores file metadata in addition to versioning information

• In addition, we have major source of one or more (federated) catalogs

• I think this confused situation will need to be addressed by some new dynamic metadata model

Metadata Catastrophe II• There are large long term metadata catalogs associated with

major applications/services– These are likely to remain as now based on traditional major

database technology like Oracle MySQLK and DB2• There are small but broadly available metadata catalogs

– Globus MDS and EDG RGMA roughly address these– Semantic Grid enriched Service catalogs as in UDDI

• We need to implement UDDI in a distributed (federated) fashion and work around its non-intuitive schema but this seems straightforward

• All the problems occur for local and highly dynamic data where key issues are:– Consistency: If metadata stored in messages flowing around, how

do we ensure consistency if it ever changes– Where is it: How do we decide where to look it up?

• My intuition is that best solution is highly dynamic lightweight database – doesn’t really fit any proposal yet!

Metadata and Semantic Grid• Can store in one catalog, multiple catalogs or in each service

– Not clear how a coherent approach will develop• Specialized metadata services like UDDI and MDS (Globus)

– Nobody likes UDDI– MDS uses old fashioned LDAP– RGMA is MDS with a relational database backend

• Some basic XML database (Oracle, Xindice …)• “By hand” as in current SERVOGrid Portal which is roughly same

as using service stored SDE’s (Service Data Elements) as in OGSI• Semantic Web (Darpa) produced a lot of metadata tools aimed at

annotating and searching/reasoning about metadata enhanced webpages– Semantic Grid uses for enriching Web Services– Implies interesting programming model with traditional analysis

(compiler) augmented by meta-data annotation

Database

SDE1SDE2

Service

SDE1SDE2

Service

SDE1SDE2

Service

SDE1SDE2

Service

SDE1SDE2

Service

SDE1SDE2

Service

SDE1SDE2

Service

Individual Services

Web Service Ports

Grid or Domain Specific Metadata Catalogs

System or Federated Registry or Metadata Catalog

Database1 Database2 Database3

Four Metadata Architectures

MessagesM M M M M M M M M M M M

Stateful Interactions• There are (at least) four approaches to specifying

state– OGSI use factories to generate separate services for each

session in standard distributed object fashion

– Globus GT-4 and WSRF use metadata of a resource to identify state associated with particular session

– WS-GAF uses WS-Context to provide abstract context defining state. Has strength and weakness that reveals less about nature of session

– WS-I+ “Pure Web Service” leaves state specification the application – e.g. put a context in the SOAP body

• I think we should smile and write a great metadata service hiding all these different models for state and metadata

Explicit and Implicit Factories• Stateful interactions are typified by amazon.com where messages carry

correlation information allowing multiple messages to be linked together– Amazon preserves state in this fashion which is in fact preserved in its

database permanently• Stateful services have state that can be queried outside a particular interaction• Also note difference between implicit and explicit factories

– Some claim that implicit factories scale as each service manages its own instances and so do not need to worry about registering instances and lifetime management

FACTORY

1

2

3

4

FACTORY

1

2

3

4

Explicit FactoryImplicit Factory

Hiddeninstances

Explicitinstances

Web Service Notification I• WS-Eventing Web Services Eventing (BEA, Microsoft,

TIBCO) January 2004 http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnglobspec/html/WS-Eventing.asp

• WS-Notification Framework for Web Services Notification with WS-Topics, WS-BaseNotification, and WS-BrokeredNotification (OASIS) OASIS Web Services Notification TC Set up March 2004 http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=wsn and http://www-106.ibm.com/developerworks/library/specification/ws-notification/

• JMS Java Message Service V1.1 March 2002 http://java.sun.com/products/jms/docs.html

Notification Architecture• Point-to-Point

• Or Brokered

• Note that MOM (Message Oriented Middleware) uses brokered messaging for ALL transmission and not just “special” notification messages

Service B Service A

Broker PublishSubscribe

Queues MessagesSupports creationand subscription of topics

Service B Service APublishSubscribe

Classic Publish-Subscribe

Publisher 1

Subscriber 1 Subscriber 3Subscriber 2 Subscriber 5Subscriber 4

Topic BTopic A Topic C

Publisher 2

NotificationServicebroker

broker

brokerbroker

Publisher 1

Subscriber 1 Subscriber 3Subscriber 2 Subscriber 5Subscriber 4

Topic BTopic A Topic C

Publisher 2

NotificationServicebroker

broker

brokerbroker

Web Service Notification II• WS-Eventing is quite similar to WS-BaseNotification and

provides service to service notification• WS-Notification is similar to CORBA event service and

adds brokers to mediate notification which has several advantages– Don’t need queues and lists of subscribers on each

service– Solution scales to any number of publishers/subscribers

• JMS well known successful non Web Service brokered notification system

• Topics defined in WS-Topics can also provide contextualization

• Expect this area to clarify reasonably soon

FTHPIS: CIE for Applications I• CIE is designed to support metadata needed by the

“galactic distributed operating system” controlling services• It can used for cases where an application naturally is

supported by a Gaggle services with a modest amount of metadata

• A new approach to Configuration files• Maintaining user profiles and preferences• Maintaining application specific metadata such as GIS

metadata • Maintain “Grading System” for e-learning• Maintaining information regarding sessions and also the

state of entities in these sessions in GlobalMMCS• Enable playback/replay capabilities in GlobalMMCS or

other NaradaBrokering applications needing fault-tolerant event storage

FTHPIS: CIE for Applications II• Three key features of FTHPIS are

– Supported in Peer-to-peer or central server role– Fault Tolerance– Context (database) is lightweight and either files or real

databases• Fault Tolerance includes

– WS-ReliableMessaging– Replicated Storage of Messages to support reliable

messaging and permanent storage for replay. Also supports performance as data locality (caching)

– Fault Tolerance metadata stored in CIE (FTHPIS)– NaradaBrokering support of replicated services where

these services are discovery, access, storage etc for each FTHPIS (include caching support – location of nearest copy)

P2P and NaradaBrokering I Server/Broker-free version to support “immediate deployment” of NB-based

Community Grids using P2P versions of Grid applications Initially: Use a broker free version of NB and file-based Web services

• If successful, add brokers in the Grid sky to achieve better performance (if broker has better network link than clients)

Service providers and supercomputer/national grid centers could sell such Grid Farm services

P2P

Grid Farm in the Sky (clouds)

NaradaBrokers

P2P and NaradaBrokering II Global Information System could start with multiple

FTHPIS style lightweight Fault Tolerant Metadata Catalogs – subscribe multiple instances of metadata service to the MetadataCatalogN topics – publish queries to these replicated subscriber topics

Then one could add DHT (Distributed Hash Table) approach (used in latest JXTA) in NB. NB nodes will have Ids that can determine where a specific content would be stored.• Provides scalable location of content over LARGE numbers

of end-points with limited query capabilities Flooding to bridge gap between DHT and FTHPIS

where queries are broadcast to multiple gaggles and FTHPIS is used within each Gaggle

P2P and NaradaBrokering III GridTorrent: Merge NB-enhanced GridFTP and P2P

BitTorrent http://bitconjurer.org/BitTorrent/ to provide WSRM fault tolerant Parallel TCP P2P or Grid file transfer• BitTorrent supports fragmented distributed files which are

natural WSRM and NB architecture• Don’t really want GridFTP server; prefer to use fault tolerant

GridTorrent metadata service (implemented as a Gaggle FTPHIS)

GridTorrent file transfer automatically provides distributed fault tolerant caching – a better RLS?

P2P and NaradaBrokering IV We have proposed building a portlet based portal to the

IOI CIE and FTHPIS In the spirit of P2P, we can propose a model where one

exposes distributed files AND streams in same way as Napster or Gnutella – each resource (file or stream) is displayed in a “metadata enhanced” ls/Windows Explorer fashion• Metadata includes updating thumbnail for streams as in

GlobalMMCS or AccessGrid Note that “unit of resource storage” could be individual

end-point (client or server) or Gaggles or even better hierarchically endpoints Gaggles Gaggles of Gaggles