Community Grids Architecture Discussion

1. Community Grids Architecture Discussion Internal Discussion August 20 2004 Geoffrey Fox Community Grids Lab Indiana University gcf@indiana.edu

2. 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

3. 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.

4. 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

5. 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

6. 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

7. 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/

8. Application Specific Grids Generally Useful Services and Grids Workflow WSFL/BPEL Service Management (“Context etc.”) Service Discovery (UDDI) / Information Service Internet Transport  Protocol Service Interfaces WSDL Higher Level Services ServiceContext ServiceInternet Base Hosting Environment Protocol HTTP FTP DNS … Presentation XDR … Session SSH … Transport TCP UDP … Network IP … Data Link / Physical Bit level Internet Layered Architecture for Web Services and Grids

9. 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

10. R1 R2 Enterprise Grid Dynamic light-weight Peer-to-peer Collaboration Training Grid Students Information Grid Compute Grid Campus Grid Teacher 4 Overlay Networks With a 5th superimposed

11. 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

12. Closely coupled Java/Python … Coarse Grain Service Model Service B Service A Module B Module A Messages Service B Service A 0.1 to 1000 millisecond latency Method Calls.001 to 1 millisecond Linking Modules • From method based to RPC to message based to event-based “Listener”Subscribe to Events Publisher Post Events Message Queue in the Sky

13. 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

14. 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.

15. 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

16. CPUs Clusters Compute Resource Grids Overlay and Compose Grids of Grids MPPs Methods Services Component Grids Federated Databases Databases Data Resource Grids Sensor Sensor Nets 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 hierarchyLines of Code  Methods  Objects  Programs  Packages

17. Gas CIGrid Flood CIGrid … … Gas Servicesand Filters Flood Servicesand Filters Electricity CIGrid Portals Collaboration Grid Visualization Grid Sensor Grid GIS Grid Compute Grid Data Access/Storage Registry Metadata Core Grid Services Physical Network Security Notification Workflow Messaging Critical Infrastructure (CI) Grids built as Grids of Grids

18. Field Trip Data ? GISGrid Discovery Services RepositoriesFederated Databases Streaming Data Sensors Database Database Sensor Grid Database Grid Research Education SERVOGrid Compute Grid Customization Services From Researchto Education Data FilterServices ResearchSimulations Analysis and VisualizationPortal EducationGrid Computer Farm Geoscience Research and Education Grids

19. NaradaBrokering Audio/Video Conferencing Client Computer Modem Server Peers NaradaBrokering Broker Network Minicomputer Firewall Laptop computer Workstation Peers Audio/Video Conferencing Client PDA Web Service B Queues Stream Server-enhanced Messaging NB supports messages and streams

20. Current NaradaBrokering Features

21. 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 Higher Level Services Application Specific Grids Generally Useful Services and Grids Workflow WSFL/BPEL Service Management (“Context etc.”) Service Discovery (UDDI) / Information Service Internet Transport  Protocol Service Interfaces WSDL CIE IOI

22. 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

23. 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 NB Brokers FastLink FirewallHTTP B1 SatelliteUDP A Hand-HeldProtocol B2 Software Multicast Dial-upFilter NB Broker B3 Client Filtering

24. 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

25. 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.

26. NaradaBrokering Service Integration S1 P2 S2 P1 S2 S1 S? Any Transport Service P? Proxy NB Transport Standard SOAP Transport S1 S2 Proxy Messaging Handler Messaging Notification Internal to Service: SOAP Handlers/Extensions/Plug-ins Java (JAX-RPC) .NET Indigo and special cases: PDA's  gSOAP, Axis C++

27. M(n) M(n+1) Service B Service A 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

28. 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

29. Custom Message Reliability Filter 2 NaradaBroker Filter 1 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 Wireless Optimized WS-RM WS-RM WS-Reliability

30. NaradaBrokering and Fault Tolerance GridFTP plus NaradaBrokering • 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 BitTorrentP2P file swapping model (better than GridFTP?)

31. Pure SOAP SOAP over UDP Binary over UDP 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) 7020 5.60

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. 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

40. Web Service Metadata and State I • The Semantic Grid and Semantic Web are important frameworks for metadata but handicapped by lack of “compelling” tools • RDFResource 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!

41. 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

42. 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

43. 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

44. 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!

45. Metadata and Semantic Grid • Can store in one catalog, multiplecatalogs 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

46. Four Metadata Architectures Database3 Database1 Database2 SDE1SDE2Service SDE1SDE2Service SDE1SDE2Service SDE1SDE2Service SDE1SDE2Service SDE1SDE2Service SDE1SDE2Service M M M M M M M M M M M M Database System or Federated Registry or Metadata Catalog Grid or Domain Specific Metadata Catalogs Web Service Ports Individual Services Messages

47. 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

48. Explicit and Implicit Factories 1 1 F A C T O R Y F A C T O R Y 2 2 3 3 4 4 • 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 Explicit instances Hidden instances Implicit Factory Explicit Factory

49. Web Service Notification I • WS-EventingWeb Services Eventing(BEA, Microsoft, TIBCO) January 2004http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnglobspec/html/WS-Eventing.asp • WS-NotificationFramework for Web Services Notification withWS-Topics, WS-BaseNotification, andWS-BrokeredNotification(OASIS) OASIS Web Services Notification TC Set up March 2004http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=wsnand http://www-106.ibm.com/developerworks/library/specification/ws-notification/ • JMSJava Message Service V1.1March 2002http://java.sun.com/products/jms/docs.html

50. Broker Subscribe Publish Queues Messages Supports creation and subscription of topics Service B Service B Service A Service A Notification Architecture Publish • Point-to-Point • Or Brokered • Note that MOM (Message Oriented Middleware) uses brokered messaging for ALL transmission and not just “special” notification messages Subscribe